I need some perspective from other raid groups on what you expect out of people. Ideally, from other guilds at about the same level we are (4 Naxx bosses down).

Measured in terms of material success (how often do you wipe, and how often do people die during pulls?), what level of performance are you used to?
How many times per week/month do you suddenly wipe because the MT "just died"? (on, say, Emps or something, where there is danger, but which you theoretically should be able to handle).
To what extent do you lose people on trash (as deaths are probably the single biggest factor in clearing speed)? Are trash deaths taken as seriously as equivalent random deaths during a boss fight?
For any particular raid death (tank or especially otherwise), is a particular person or set of people responsible? Or does the rest of the raid simply have to chalk up the error to "the healers" and hope it doesn't happen again?

How do you identify the strong and weak healers?

IMO, the worth of a certain healer is usually determined by how often *they* die. Especially further into AQ, things like twin emps/ouro/cthun where you are constantly moving out of the way or watching your relative position to others is usually a good indicator.

As for the healing part, I'd say it's determined by what you are pulling/killing. You can expect mage/fury dps warrior death generally at least at some point where there is alot of AE trash, but too many and you know your healers aren't paying extra attention like they should be.

If it's an unusual class that shouldn't be dying, say, hunters for the most part aren't taking enough dmg, you know people are watching football or some other crap instead of keeping an eye on their group/raid.

That's really the only thing I can think of. If the members of your raid who aren't often taking enough dmg to outright kill them are dying, and if the priest themselves seems to hit the ground more often than not, they probably suck. At least that's been my experience.

Gauging the performance of individual healers in 40-man raid situations has always been far more difficult than that of tanks or DPSers. Whereas an individual DPS class can be ranked against others, with healing it seems much more binary: sort of a pass or fail situation: if the tanks lived and you beat the encounter, the healers passed :-)

As a healer, I can usually identify quite easily what went wrong if a tank goes down. If they (the tanks) need to reposition or change their tactics, I'll tell them so. Conversely, if it was a healer failure, I'll be the first to stand up and say so as well.

If your going to start a tank vs healer war id suggest getting the tanks to /combatlog and run parsers then analyse a few. If you said healer A,B,C on MT1 then mt dies 10 seconds into pull and MT1 only got heals from A&C asking B WTF is going on can be useful. But if you yell at all healers then it can get out of hand.

There was a tank in my guild that used to say WTF no healing every damn raid over vent so we started half seriously telling new healers they wernt allowed to heal that person.

A good simple thing to do is make your tanks enable SCT with healers name showing when they get healed and heals in combat log with timestamps. I also like to have them run the healtracker mod from sartrinas page which tracks who healed them for how much.

As far as trash wipes, the biggest thing i find is people not knowing where everyone else is going, its very easy to get out of range. I remember a MC lava pack pull where one tank ran forward i ran forward to heal them,then i counted 4 of the 5 mobs hitting me in the same second in my combat log because no one else had aggroed them.

Using a mod which tells you which healers are targeting yourself if your a tank, or tanks if you click on them can be handy but some people switch targets a lot or select heal then target. I find nightwatchers incoming heal monitor my favourite way to let everyone know who is healing who. It can change the ctra window of a healer to their target.

Do you assign healers on trash?

Assigning blame for healing is pretty pointless. That was a mistake, please fix it, lets move on, is generally more productive.

You're welcome to disagree, but you will get much further helping poor healers improve (or recruiting new ones) then trying to develope some metric by which healers can be ranked on an absolute scale. That said, here's some general guidelines.

In general - Your paladins (if you have them) should be topping the effective healing.
Your priests and druids should be interspersed, maybe one or two beating out the worst geared paladin.
Overheal above 40% is bad, on our server. On your server you may move that number up or down (we're battlegroup one, we consistently crash twice per weekday raid.)
On trash:
Watch for preemptive shielding before mages start AoE.
Watch for correctly timed blessings of protection.
Expect your druids to fall behind on situations where the mobs are not tanked, or to die, depending on how adaptive they are - If you don't see druids dropping their argo onto the tanks adaptively, help them learn it. Learning when you need to bear or cat is _very_ specific to the trash and the room you're in when you argo as a druid healer.
Monitor decurse counts - in particular, look for druids/priests pre-casting abolish on likely targets.

Lastly,

There is very little trash that requires 15 healers. Don't be afraid to tell your priests to dps, or your druids to tank, if the trash is such that doing that makes it a faster clear. The post-emps trash is a good example, 10+ tanks and 10ish healers is a much better solution than 5ish tanks and 15ish healers. Similiarly, the trash in the deathknight wing can be healed by 3 paladins - tell the rest of your healers to dps so you don't spend forever fighting the legions of crappy deathknights.

One of the things we've tried to start doing is concrete assignments for everything that allows for it; we've been notoriously horrrrrrid on trash fights, and simply decided to put healers in groups and give em the "fuck up and we frown at you" face; at this point, we take trash tank deaths very seriously since its time wasted and frustratingly needless repair bills.

When the raid is universally on top of its game, random tank deaths almost never happen (possibly on twin emps, but becoming rarer every week). We have bad nights, but those are usually the byproducts of the entire raid just being in a funk, not a specific group.

We've also taken to using healing efficiency and overhealing meters, and though we don't take official action about it, when someone is sitting at 50% overhealing and everyone is looking at them funny, most develop a desire to improve.

Honestly, breaking assignements down to very specific roles has worked really well for us, since it promotes accountability and reduces confusion. One of the biggest problems we had to overcome was non-healer raid leaders laying blame on "the healers" for fucking up, since the general response to a warlock making a blanket complaint generally engenders a response something along the lines of "fuck you too buddy." I can't speak to the attitude of your guild, but I'm finding that a frown and a "you can do better than that" goes a long distance.

As a fellow denizen of the hell that is Battlegroup 1, I feel your pain.

This is a good suggestion, although it requires additional management.

We generally do trash assignments as follows, and work with a "call your tank in heal and off we go" method to speed things up.

Tank - Paladin/Druid
Tank - Paladin/Druid

etc

Mages - Two priests
Rogues - Two priests
Warlocks - Shadowpriest.

Hunters can, and should bandaid. One priest assigned to shield whoever is pulling.

We were on pace for a full aq clear in 2.5 hours, until the server keeled over and we all went to watch megaman time attacks.

I'm starting to think that some of the goofy shit we do when the server crashes is more fun than the raiding sometimes.

Pointing fingers without just cause is just going to make your healers reroll something like a hunter.

Combat Log analysis is the first step. As others have stated, its a simple look to see if everyone is healing tanks as they should be or if a damage spike was simply too big and too fast to reasonably expect to heal through. If healing wasn't happening, why? If the Emps, are the healers OOM because they don't have a reasonable plan to last through the fight while dealing with the damage spikes?

Do your healers have one or more leaders that give assignments, offer advice and ask people to step up when they aren't performing? Are your healers sitting in their own channel communicating healing specific information? Advice from a fellow healer goes much further than random DPS class whining about the healing to the whole raid.

Strong and weak healers? Meters tell part of the story, usually gear. 5 mans and PvP tell more. At your level of gear, thats 5 manning UBRS and intentionally pulling adds to see how the healer responds. PvP tells you more about their taste for that part of the game, but healers that heal in PvP usually learn some good survival skills.

Overhealing is very fight dependant. More than 20% overhealing on trash mobs usually means some healers should be DPSing. Overhealing on spike damage bosses is normal and isn't a problem unless healers are OOM or using way too much consumeables.

Deaths on farm content should be frowned upon. Many are avoidable through paying attention to healing, others aren't because someone is being a monkey healing to keep them alive is going to kill tanks.

If you're still setting up groups with a tank and healer in each group those healers are responsible for their tanks. If you're optimising some groups there should be a healer leader making assignments so the raid leader doesn't have to worry about it.

It's nigh-on impossible to tell a healer's skill in a large raid group, except as a general thing (i.e. boss down, no deaths, the healers passed), unless you're a member of the same class and monitoring what they're doing yourself. SWStats monitoring the healing they do *might* be a useful tool (I'm not sure on what exactly SWStats can do), but even then that won't show the clutch shields/NS HT's/BoPs etc.

Vex nailed a good point as well, if the healer themself is dying something is wrong (either they're plain undergeared, wearing the wrong gear, or they simply can't cut it).

Also, it's been my experience that healers that PvP gain instinctual positioning and reactions that a pure-pve raidbot probably won't have.

I couldn't agree more, I very nearly switched mains to my Hunter because of finger-pointing in my old guild by the raidleader/maintank (i.e. when he died with Nef at 19%, that's not the time to be yelling "Where were the goddamn heals!" because at that point I (and the other eleven healers) was/were busy trying to got those heals to the offtank).

What's your trash healing strategy?

That's the first thing you have to look at. A lot of trash deaths can be attributed to either all the healers being busy healing someone else, or healers slacking in the anonymity of raid healing. I've known plenty of perfectly good healers who are terrible, terrible trash healers unless you assign them a group and tell them explicitly "if anyone in this group dies I'm blaming it on you". Otherwise they go semi afk because usually someone else will pick up the slack, and if not, hey they can be ressed after. It's only trash afterall... an attitude I hate personally, but it's better to change your strategy to keep a good healer on their toes during trash then to toss them because they won't heal well in an FFA situation.

Otherwise you can look at the actions made by the players. Sw_stats is good for this as you can actually count up the number of actions they took over a period. You can also see the spread of people they healed. If they're set to randomly heal the raid and there's only a couple people high in their list then they've been slacking. Then take a look at overhealing on trash. Now, really low overhealing means either everyone else is slacking or they are so don't worry about there being overheal, but look for those with massive overheal compared to others. Those are the people mindlessly hitting the lowest EM target and healing them. If you have too many of those, people are going to die.

If the problem is tanks dying on trash that's an easy one to fix. Make sure everyone who is expected to take damage (aoe'ers and tanks really) has a healer or healers assigned to them. They don't have to be on them 24/7, but they have to know that it is their primary responsibility to keep that person up. If you don't do that you get the phenominem of everyone healing someone else all at the same time, expecting someone else to heal the tank. And if the tank then dies... hey you have someone to blame. :P

EDIT: Addressing your points more directly:

- Wiping is pretty rare on farmed content, but I'd still expect 1 every fortnight or so. Often it's a case of everyone not taking the raid seriously and 1 wipe is enough to kick them into action again.
- That's the main way to wipe, the tank "just died" and nobody knows why. If you are a DPSer you need a healer to tell you what happened if you can find one objective and analytical enough. As a healer you can get a feel for why a tank died, and will often have a "he's gonna die" feeling right before it happens because you feel the others slacking or too many regenning at one time. Asking the tank CAN work, but do it quetly and be specific in what you want, like how many heals were they getting at the time, did they get a chain of big big hits, etc (get them to check their combat log too).
- Generic raid trash deaths are usually attibuted to people doing stupid things and getting what they deserve. Tank deaths on trash fights are usually attributed to their healer doing a poor job. It varies wildly on how everyone is acting on the day and who is leading the raid (which affects assignments as well as how hard healers are being leaned on).
- Again it depends on the raid leader, when the healing assignments are done properly it's very easy to pinpoint who fucked up and that person gets a quality 1on1 with the raid leader in tells. If not then yeah... the generic "healers pick up your game" is all that you can do.

I find the post emps trash as good measure of healer quality. It fun to see who the Qiraji champion runs after a knockback, and I can't count the number of times I've been nailed by a loose slayer(after fading etc.) There's lots of damage going around, and seeing who reacts to mindflays can be a another good healer test. I suppose it also teaches positioning with the on-death mana burn bit too.

I just wish there were like 4 packs instead of 43646 ( or so it seems).

Judging a good healer is very difficult in a 40-man raid situation. For starters, "Healing Done" meter is an inconsistent indicator of a healer's skill.
I know some bad healers who enjoy being on top of the healing charts.
Healing is all about timing. A well timed PW:S on a rogue which gives him that extra second to live while the druid's slow heal lands on him could've eventually made the difference on a 1% Vael, Emps or Patchwerk fight.

I firmly beleive that healers can be judged far more reliably in smaller raid groups, and especially PvP. The dynamic nature of PvP is perfect to simulate the dynamics of high-end encounters and especially trash pulls.
With the auto-raid invite system for the BGs, PvP healers are expected to "keep their eyes open" as well as keep an eye on the EMonitor.
Also, PvP gives healers the ability to prioritze their heals. I would rather heal a warrior at 50% hp whos beating (and getting beat) on the enemy flag carrier, than a hunter a with 20% hp shooting from back. A mindless EM-spamming drone would not be able to make such quick combat decisions.

Coming back to PvE.
If you are having problems clearing trash, I found out that the most effective, fastest, smoothest way to clear trash is to let each healer heal their own group.
Many raid leaders prefer to bunch up all their healers in 1-2 groups, thats fine for some encounters. But for trash, its best for each group to be a self-contained unit responsible for its own survival. Having this system gives the further advantage of seeing which healers are slacking, or just plain suck.