Inner Focus + Divine Hymn is full of win and ponies. On Ignis and XT, I've done 110K+ effective healing in one Divine Hymn cast, for no mana. 80-110K seem pretty typical for my guild's Holy Priests. It's a "get out of big raid raid damage for free" card.

In Disc spec it is even better! I'm getting tons of crits and Divine Aegis is proccing all over. Just awesome! Half of the raid is in my bubbles!

After one disastrous attempt, we ended up trying the pull with 5 tanks... a little absurd, but it went smoothly.

Hunter misdirect to the MT who was LOS from boss pathing, DPS was extremely light for the first ~5 seconds or so to ensure the tanks could retain threat on their target.

2 Holy Paladins -> Warrior MT
Discipline Priest -> Prot Paladin
Restoration Druid -> Bear Druid
Restoration Druid -> DK
Holy Priest -> Warrior

All tanks blew their cooldowns on the pull, with myself (Disc for this fight) & our Holy Priest popping PS & GS where needed. There was some issues with spike damage on the Druid and DK tank, but tossing out a few shields was more than enough to help the other healers catch up.

We didn't wipe once on the initial pull after putting this setup in place. However, forgetting to move the healers into a Shaman group for Tremor Totem most definitely did =P

I was raidhealing (13/58 holy priest) on The Assembly of Iron and I can't stress enough how great PoM was working during the phase all three mobs were up. PoM was 30-35% of my total heals and I had a HPS around 3,5k-4,5k. I were flashing x3, throwing away a fast PoH on groups that needed it the most. Using CoH and PoM as soon as I could. I went down max 50% on mana but had time to regen alot before I acctually needed to throw out any heals again. I was telling the other 2 priests (both disc) about my thoughts and on every other attempts the priests were high up on the meters. I know the meters isn't what counts, but it's nice sometimes to have data to analyse and hopefully helps you improve.

Anyone got any advices on phase 2 and 3 on the same fight?

I finally gave in and picked up Lightwell for Vezax. It's nice to drop in (or click before you enter) a vapor cloud to heal up the damage you take. I was able to withstand 6 stacks of the (de)buff, regenerating myself almost back to full mana. We used a "vapor rotation," subbing the healers into clouds while others healed the tank. I'd advise shielding yourself beforehand, though, if you're going to stay in for that long. Problem is of course when you get targeted for Shadow Crash while you're scrambling to get your mana back up.

Unrelated, but I have fallen in love with Glyph of Guardian Spirit. It was worth getting gouged by the 3.1 AH glyph prices!

I must say i'm really happy with Disc healing so far. I tend to switch specs a lot between fights and wipes to try them out.
Thi is my experience so far: we ran 6 healers, 2 priests of different specs, 1 druid, 2 shamans, 1 paladin.

Leviathan: uuuh. choppa! (hey i can heal, can't it?)
XT: Holy just felt much more useful here. we had 2 holy priests laying down lightwells for melee. i was also healing the offtank - body and soul to get him in range for akward spawns was great.

Razor: again, i was holy to begin with but i tried disc the other time around and it felt a lot smoother. shielding + grounding totems took care of almost all random damage during the fight.

Ignis: This was a close one but i felt holy was a little more on the ball here. stacking serendipity before jets and then popping a fast poh + coh after, SoL flash heal + another poh resulted in a huge throughput.

Assembly of iron: I went with holy here since we killed stormcaller last. BaS shield for a slow melee saved a few lives (well one but multiple times) and coh + lightwell was just great on tendrils.

Kologarn: again i felt like holy had the uppe hand with lightwell and CoH. BaS shield on the one getting chased by eye beam made things a lot easier.

Auriaya: started as holy and it was by no means bad but coh just wasnt cutting it so i switched to Disc. I kept shielding everyone that took damage from the defenders pounce, never getting interrupted. i didnt heal anyone to full during this time but people stopped dying due to interrupted healers!

more to come

Disc or Holy really depends on your other healers. Our raidcore has a lack of paladins, but we've had 4 healing priests on many kills. I'm dual-specced disc/holy, so I try both until I find what works best on each encounter. On fights like XT-002 and Hodir, I've found Holy superior, just because of the massive healing you can dish out with PoH and CoH. On Ignis I was disc, and I found it amazing how I could shield all 3 tanks while in mid-air, Penance whichever needed healing the most after landing, and then healing another with a hastet GH. On Kologarn I was disc again, and it really, really helps keeping both tanks up when people start dying.

I see here that some people prefer disc on all AOE fights, basically shielding everyone pre-emptivly. I've prefered Holy on the fights where we have enough tank healing, but I can really see this working. Will have to try it.

Like the above poster said, on Auriaya disc really shines. You won't be interrupted, and will save pretty much everyone. You can even save people that are being feared into void zones.

I felt the Iron Council was too easy to really make any difference, but I'm sure hardmode will change this. Same with Freya, not really healing intensive and maybe the easiest boss so far.

On Thorim I'm not really sure what I prefer. Druids are obviously the healer of choice in the arena, and Holy have CoH which is pretty good. I can really see a disc priest being very useful though. I was in the gauntlet on our kill, so I didn't get to test it out.

Divine Hymn and Hymn of Hope are pretty sweet also, I forgot to test a hasted DH on Hodir, but I assume it works. Also, GH glyph is so amazingly good it's hard to pass it no matter what. With two Holy priests, you can set up GH rotations on the MT during tough phases, like Hodirs Frozen Blows or Ignis' Flame Jet.

I'm very happy with 3.1 from a priest pov so far. With a Holy/Disc dualspec, I really feel we've become a jack-of-all-trades class, except the master-of-none part is removed. I wouldn't be surprised if we see some nerfs coming in, GC has already said that PW:S will be looked into. Will be interesting to hear about what spec other people prefer.

Hopefully this will help people a bit, but here's what my strategy was on every fight.

Razorscale (Disc) - Shield spam. Since we had 2 holy pallies, I didn't think that Flash Heal would do anything useful. My strategy was very simple - I don't give a flying fart if anyone gets hit once. I only care if people get hit 2-3 times. I just bubbled anyone who got hit, and then if I saw my bubble fall off, flashed or penanced em. Penance was great because people rarely got hit too often (and the Realm was short a glyph when we did this, so it's only gotten better).

Ignis (Holy) - Pretty conventional Prayer of Healing spam. CoHed in the air, float a PoM before, renew and shield the tank. Flashed people in the pot. Prayer of Healing spam is full of win.

XT Deconstructor - Prayer of Healing and Circle of Healing.

Iron Council - irrelevant, I could have been shadow for all the healing there (I vaguely recall being holy because I think the tank got wings for a few falcon punches, but it might have been PS, it was quite, quite late)

Kologarn - Holy, because CoH on the gripped people is made of win, and PoH gets the raid up fast. Messy fight. Keep Prayer of mending off the GCD. It's mostly just about getting the raid up and using PoM to keep tanks higher than they should be. I almost want to be disc for this, even with CoH, bubbling the Gripped people is just as good, and Penance could be nice for when the debuff gets high.

Aureya - Yiyiyi, that pull. I lost a bear with PS on him. Disc, I bubbled all the tanks and we used cooldowns A neat trick I found when I did this on normal mode was that spamming Holy Nova on the cat adds can quickly get rid of many of them. Holy Nova is hasted with Borrowed Time and doesn't consume it, so feel free to shield the tank and then spam 3 quick novas. Other than that, I think I Mass dispelled once for a fear, it didn't do as much as I wanted it to, and after that my ward was kinda dead.

Hodir - Holy. So much outgoing raid damage. PoH regularly, CoH regularly, PoM all the time, etc.

Thorim - Disc, went gauntlet. It was late and we kept losing people to stupid (example - I died to left right, we lost two people to a mob going untanked, we lost a tank in the gauntlet because 3 healers failed to react to the tank walking around the corner and pulling, we lost the middle because of, well... someone said 'oh *#!@' in vent and then a big lightning bolt ate us). Once we got it down, it's just a tank and spank. Disc was huge because bubbling the tank lets you push unbalanced blows a bit past where you could otherwise go (our last blow left the tank at 4k health - with my bubble gone, next one we were going to blow cooldowns but the DPS was good (even with a few dead) and we got him.

Freya - This fight isn't Sarth+0 easy, but it's still easy. We're definitely doing it with an add next week (well, maybe not, coin flip if we want the badge of conquest that we're not going to get). CoH is its usual pile of win here, but Body and Soul really proved itself on the kiting (I think it saved a hunter at least once). I was a bit panicky about trees after the tank got one shotted and he tended to develop wings at odd moments, but nothing ever came of it (after that the dps blew the hell out of them, and GS never got consumed). I could see disc being useful (Detonating lashers, I PREDICT RAID DAMAGE) but I think the hard mode mechanics are going to make or break the fight. We got to see at least one of them after she had zero stacks of the debuff (she did a little move that wiped the raid. Since it wasn't in any of the strategy guides or videos, and didn't happen again, we're guessing it was a hard mode mechanic that we got to see. We're not supposed to discuss hard modes on this board, but I think it's safe to say that the fight will get a LOT more movement and positioning intensive.).

Mimiron - GS was win on phase 1. Our phase 2/4 strategy was highly unconventional (most people say spread about the room), but lets just say Prayer of Healing. A LOT of Prayer of healing. Tons of Prayer of Healing. I think it was about 50% of my healing, and that's with me never using it in phase 1/3 (I didn't do much phase 3 besides follow the add tank around for B&S and wings if the add got too close though, phase 3 is a mana regen phase for healers).

So I have some questions on how everyone does a fight. My guild just got to Mimiron last night and everyone was dreading it. I thought Iron Council was going to be a hard fight to heal and I was topping out at 5.6k hps in phase 1. But Mimiron is a whole different story. As it is the first phase is pretty easy saying we have 3 holy priests in our raid we just pop wings on the main tank every cd (two of our priests have glyphed GS which is very nice) and just heal through the dmg of Plasma Blast. The second phase is where it gets very hard to heal. Pretty much the entire raid is taking 2-3k dmg each it seems and its hard to keep order on who to heal. I would like to try and get some advice on how you guys heal this and what way we should go about this. Our usual raid make up for healers is 2-3 Holy priests 1 disc priest 2 holy palidians 1-2 shams and 1 resto druid (changing from 7 to 8 healers sometimes but not often).

Spit your raid into 4 groups. Melee, and 1 per quadrant. Get the groups to stand basically *not* clumped, but close enough for CHeal bounces. Split up your holy priests and resto shamans into different groups, and make sure there are at least two healers per set, not including the melee clump.

Then just spam your face off. If anyone gets hit by Arcane Barrage, they're dead, so don't take responsibility for that. Just heal the machine gun damage, and pray. As an aside, this was the first fight that made me go "holy crap, Healing Focus would be nice right about now".

Just to give you an idea of how it really depends on your raid comp...we had our only priest as disc for that fight. Had him heal slag pot and help bubble OTs and MT, while keeping insp up on the MT. 2 shamans on raid, 1 druid healing ots + raid. 2 pallies on MT beacons on OTs. Since we only had 1 priest we voted for the 3% reduced raid damage over holy spells.

Point is there's no reason both either way won't work. This is a nice time to be a priest. :]

I know that there's a lot of fights where it might not be truly necessary but I really get on my other healers with they skip out on these talents.