Vek'nilash, Krosh Firehand, Zerevor and even heroic Razuvious - all tanked by me. But neither of those require any resists at all, with exception of Vek'nilash if you are still 60lvl.

Please remember that at both mage-tank encounters in TBC resistance was worthless. Fire or arcane resistance had no effect on the dmg from krosh or council.

Perhaps there'll be more fights along the lines of SSC Leo for warlocks. Mages will be a natural choice for resistance tanking. The only problem I can forsee in these circumstances is keeping threat.

As a side note Molten Shields and Frost Warding provide similar protective benefits, as do the glyphs for the improved wards. I'm currently using a Fire raiding build that has both [what ELSE was I going to take to jump from Precision to Icy Viens?] as incidental talents, and in fights involving Fire or Frost the wards become amazingly powerful. And I don't just mean 'hey, look, I reflected that Pyroblast back into his FACE!', I mean as raid DPM/DPS are concerned. Obviously, most fights won't see a benefit here, but element heavy fights allow you to turn direct damage into DPS potentially worth the cost of the cooldown and any damage into potential mana gains [like Magic Absorption can]. The idea of the shield paying for itself or boosting your DPS is clearly a fight specific, RNG based trick, but I have actually used it just in Heroic Nexus and noticed significant returns from using Wards: Instead of being at about 1/4th of my mana at the end of the fight, I was nearly topped off and never had to use Evo (I was still relearning my casting cooldowns and priorities, so that meant a lot at the time ^_^; ).

Assuming you're passing up Playing with Fire [because playing with fire can get you kilt!], you can get a reasonable raiding build that combines the benefits of all this together, but sacrifices AoE potential to become specifically a single-target raid DPS bugger that has less to fear from magic dangers in fights [like mana drains, raid-wide magic damage, etc.]. Note that this IS effecitvely a gimmick spec, despite having most of the DPS boosters fire can take. You lose Playing with Fire, both fire AoEs, the possibility of insta-flamestrikes, any survival or DPS Fiery Payback grants, range, BT, and gets no Blaz*cough*Fire Blast CD reduction.

I'll bite on this thread a little ....

I'm not saying it would be in any way the best use of resources / slots / points etc .....

BUT you could get your resists over 300 by using the Flask (which does stack w/ totems or MOTW) and some Void Spheres.

I've never specced arcane myself so I have a somewhat naive question - does the Incanter's Absorption talent work off resists or only off damage your Mana Shield absorbs?

It does not work off of resists, only absorbtion effects (Sacred shield, mana shield, frost ward, fire ward, ect)

I don't believe that frost, fire, or frostfire builds need mana. With proper replenishment I've never found myself even needing to evocate, even on Sarth +3 Drakes.

However with an arcane talent build this talent is probably manditory.

As a frost and fire spec, you might as well get it, not so much for the mana regen, but for less strain on healers. Although atm CoH and WG make healing a joke, but when its nerfed its going to be hard on healers and making it easier on them with 2 talent points if you are putting in arcane anyway is a good idea imo.

This could easily be fixed by a steal-able threat generation buff.

Well, I tried out a magic /incanter's spec tonight and did 10man naxx. We had some new people and had trouble with tanking zelik and blamaux, so i went back there and tanked. Zelik was painful, but blamaux I was resiting 1/3 of the dmg from every shadow bolt.

And there were actually a lot more fights with chances to pop wards and mana shield to absorb some damage and boost my spell power. Sapphiron obviously, and frost ward during KT worked well during the frostbolts that came out occasoinally.
Maexxna I mana shieled and grabbed te spider adds. AoE burned them down and gained a decent spell buff.
Thaddius I popped mana shield when polarity got highly stacked on one side (6-7) and absorbed the chain lightning for some nice buffs.
Grobbulus I popped mana shield when I got injected and came back to the fight with some extra spell dmg.

During sapphiron it helped with survival a lot. With a short evocate cooldown, I used frost ward whenever it was up, and if blizzards got bad I would also pop mana shield (since mana shield scales with spell power, i got extra protection for keeping frost ward up before hand).

At any rate, I was quite satsified with speccing for absorption for raiding; I ran some BGs earlier in the day and it was a great boost there as well.

However, I did give up Icy Veins for the spec, so I'll have to try out a spec this weekend using IV instead of absoprtion and see how things are.

Considering the global cooldown you spend casting the wards or mana shield, dropping IV just to pick up absorption is certainly not a good idea from a PvE point of view.

Magic Absorption is interesting: it really is a fun talent we'd all like to have, but it can be frustrating to squeeze 2 points free for it from a DPS focused Arcane build.