We switched things up in Hyjal this week and had me tank Anetheron. He's not a very complicated boss to main tank; just catch him as he walks in the door and hold him in one place. (The complicated tanking is the off-tank picking up the infernals). But boy does he crush hard. And that presents a real problem for the T6 bear tank.
The first line in the graph above shows my health. My scary, scary health line that rapidly dropped near zero three times. It's a tough fight to heal; there's a lot of raid damage and the Carrion Swarm debuff screws up some random set of healers. My gear's pretty good: 20k health, about 74% armor against bosses, 50% or more dodge. The problem is Anetheron crushes and a bit of bad luck can quickly get you near dead.
That first time I almost died was three hits in 1.2 seconds: 3800, 6500, 5400. The second time was three hits in 0.9 seconds: 5200, 4900, 5600. The third was four hits in 1.3 seconds: 3200, 5500, 5700, 3800. Each time, 15k+ damage in one second. That last case was the nastiest; the second hit was from the Carrion Swarm spell.
Sadly, bear tanks don't have a lot of options to stay alive when a fight goes bad like that. I saw myself dying there, knew I was in trouble. But what can a bear do at the moment of crisis? We don't have Last Stand or Shield Wall. It's nice to use a dodge trinket but that only improves your luck a little bit. I did save my life once with my new potion / healthstone macro; but that wasn't much good that last near death because of the Carrion Swarm healing debuff.
The other option I've been using to stay alive when tanking is not tanking at all. Basically a T6 bear can build so much aggro over the rest of the raid that you can stop attacking for 20-50% of a fight. If you're not attacking the boss won't parry you and so you won't get a riposte for a second quick attack. You can see me zen tanking in the third line of the graph above: my DPS out goes to zero twice. Taking a closer look at parries in the log I see the problem in my first and third near-death; one of our other melee DPS got himself parried a few times. (Surprisingly, none of the times I got parried led to any problems.)
Bottom line: in T6 raiding, crushes + ripostes lead to very spiky damage on a bear tank. Just a little bad luck and you get three big hits in one second and you're almost dead. Honestly I have to say a warrior tank seems a better choice for the T6 bosses that crush. They can prevent the crushes (usually) and they have some very powerful abilities to use if they're about to die. Bear armor is a big help in T4 and T5 raiding, but the damage numbers start getting so big in T6 that 75% mitigation is not enough.
Maybe the solution is to get to 25k health so you can survive one more hit, but that's going to cost a lot of dodge and thus require a lot more healing. Me, I like going DPS for some boss fights, druids are all about the versatility.