Recently I've just been doing pure blow 'em up groups, which I handle moroes via the expident of 2 min pvp trinket, BoP and DS with clickoffs, and tank all the adds (minus one or two like the SPs maybe), and he's dead well before we go through that, so this idea might be a bad one for you:

I either tank with a shaman in my group with Grounding down, low/light aggro, double threat trinkets equipped, high +damage/low mitigation gear. I start of 'lightish' and we burn him steadily, about 10 seconds in a mage clicks off salv and starts attempting to pull off me. If he pulls, he kites till the pull/aggro dump, if I get 'tombed' the tomb snags the grounding (I still get threat wiped) then tap one trinket and go crazy while it chases after the mage. I can usually catch back up before anyone else pulls or the mage dies (or he dies). Repeat for the second mob.

You have a way to single tank Spite?

Jumping in and out of the red beam should work if my memory isnt playing tricks on me. Something like staying out untill the buff is about to run out and jumping back in then I think. Never did it myself, but thats what Im being told.

That does indeed work fine for tanking one phase, but unfortunately the Nether Exhaustion debuff you get after the beam effects fades is long enough that you'll be halfway through the next beam phase before it expires, meaning you need a second person on the red beam. Well, unless your DPS is extremely conservative on use of the blue beam because you keep aggro normally, but that isn't a particularly wise idea.

I single tanked spite last night. It wasn't hard. You need two people to cover the second red beam phase, but they don't necessarily have to be tanks. In our example, it was a fury warrior and ret paladin. Fury warrior gets the first half and the ret pally got the second half. For the first phase, I just danced the beam -- moved off for a couple seconds, let it stack to three or four on netherspite, then took the beam for five seconds so those stacks disappear, rinse, repeat. Ended those phases with over 15k health; no fear of death.

Oz isn't too bad either. My kara group is typically pretty well rounded; fire mage for Strawman, warlock for Roar, no tank on Dorothea, and I pick up Tito and Tinhead.

Moroes, like I said, is easy if you keep up Blessing of Sacrifice on the second in threat. (plate is preferred for this; fury wars have an easy time getting second w/o salv =P )

Tanking as holy

I've searched (and read most of) both this thread and the healadin thread and didn't find the answer to this question, and I think this thread is a more appropriate place to ask it:

What can a Holy paladin with a handful of tanking talents (for example something like Talent Calculator - World of Warcraft) expect to be able to tank, given an appropriate set of tanking gear, but not "outgearing" the content? I'm thinking of things like Tidewalker adds or ZA, when guilds don't have access to a full-time prot pally.

You linked something very close to a normal holy (PvP) build, while I expected something like 20/41/0 to be able to tank ZA.

Anyway, with that spec you can tank anything that well, hits as a girl.
ZA regular trash is way above you unless your prot gear is t6 quality and I'd strongly recommend doing tidewalker adds in healing gear with that spec, getting healing agro and keeping yourself up with some help from another healer.

I can see a prot spec with holy shield and the rest in holy working decently if you slightly outgear the content or are facing normal trash, but I strongly doubt you can tank anything of much meaning in ZA/SSC with a full holy build (which is what you linked) in prot gear.

Since you mentioned ZA, can you say more precisely what exactly you want your role to be there? Something like dragonhawks and non elite AoE lynx can be done with 0 in prot as long as your gear is good enough.
I have to admit though that the only thing I've tanked as holy (my tank gear is t6 quality though) are lvl 70 normal instances and the ZA AoE trash/dragonhawks. But from my experience in speedruns (which I MT/OT as prot), I couldnt see myself tanking most trash without a decent prot build. (mostly for holy shield and +sta. AD is nice but can be avoided)

Specifically what I'm concerned with is AOE trash - Morogrim murlocs, Eagle Gauntlet, Jan'alai adds, Solarian trash+adds - and whatever similar stuff is in T6, because I'm not there yet. This sort of trash is much harder to do without a paladin tanking, so I'm wondering just how much a holy pally can handle when our prot pally is unavailable. Do you have any specific tips for holy pallies trying to tank? You mentioned doing morogrim murlocs in holy gear - what is that advantage of that over prot gear?

This is going a bit off topic, but spamhealing a lifetapping lock with imp RF right after the earthquake is guaranteed agro on all the murlocs. Once you start taking damage, switch to yourself and have another pala help out on yourself (and let him put a BoSac on you). I've done it both with a prot pala and like this, and assuming you have some decent pvp healing gear I prefer this method. (obviously, a stack of lifeblooms when you have a resto druid makes it even easier)

edit: anyway, as I said in my previous post, AoE trash is definitely doable. Only thing I'm not sure of are those packs with 5 elite lynx. (no idea if you classify that pack as "AoE", but we do)

I've bolded the key part there. The reason I have Kings on my Paladin and Improved Demo Shout/Improved Thunderclap on my Warrior (for progression, anyway) are for those occasions where there is no one else to provide those buffs for me.
There are times when I will be single tanking a boss on my own, (Gathios is a great example of this) and I may not have the luxury of a DPS warrior to keep those debuffs up for me.

Same scenario with my Paladin. There may be times I would prefer to buff Kings on other raid members so that another Paladin can give them improved Blessings instead, or be able to make sure I can buff myself with Kings if I want the extra Stamina.

For me, being a Tank isn't just about taking the view that "someone else should be doing these things for me" because raid dynamics don't always allow it. What do I do if the DPS warrior I'm moaning at to debuff dies, and all of a sudden I lose those debuffs? One talent point spent which can increase your raid synergy at no real cost to yourself for most builds is a win-win situation.

I tank the birds (not warriors if I can help it), non-elite lynxes, and Jan'alai hatchlings (8-15 at a time only) in healing gear, and I have no gear from 25-mans tier 5 and up. The reason I use healing gear is largely because I'm more useful. My self-heals more than compensate for the lack of avoidance and I don't need to switch armor and drink when there's nothing to tank. Concentration aura, consecrate, and holy light are all I need for those roles. When I tank the elite lynxes, however, I do use tanking gear so they don't smear me into the ground. (My spec varies a bit, but right now it's >this< one.)

When it's possible for a paladin to completelly trivialize MH I'd say that's quite a change. Well geared protadin only needs the other tanks to keep the AoE alive (fair bit of spam healing required for abo waves but doable). Plus they can tank pretty much anything that doesn't require spell reflect. They, just like ferals, aren't just a gimmick anymore, they're actually almost as good as warriors plus some extras. I'd say that at this point you don't need more than 1 prot warrior. Fill the rest up with a paladin tank and then ferals.