So, I got stuck tanking tonight in Throne of the Tides. I had initially queued up as feral kitty DPS and that's what I went in with after a 40 minute wait for the random dungeon at 81. The initial party composition was:

Warrior Tank
Paladin Healer
Shadow Priest
Mage
Me (kitty DPS)

The warrior... just wasn't very good. He never marked a skull, never called for CC, and the first few pulls were epic chaos. Mobs everywhere, he only held a single one while the others were off beating on DPS or the healer. I think part of that was gear, he was still wearing a lot of 150-175 item level pieces from Wrath zones. This is bad, because you can generally pickup a good number of BoE greens from the Cataclysm zones for cheap at the Auction House and boost your stats/threat quite a bit. Those pieces are all in the 270-285 range for item level.

One of the pulls, warrior tank goes down. I shift into bear form and we take the pull down. My first inclination is still to switch to bear, even when I'm in kitty form rather then combat rez. Mostly because I was still top threat on a lot of the stuff and when things get crazy, it's time for the bear suit. So we survive the pull, I rez the fallen and switch back to kitty form to DPS again.

Shadow priest decides that the warrior just isn't cut out for it - and bails. We get a rogue to take his place.

First boss is Lady Naz'jar. Warrior tank gets smoked early. I switch to bear and pick everything up and we start killing things. Somehow we pull it off with only the mage, paladin and me alive.

I go back to kitty form, because I really don't know Throne of the Tides well enough to tank. And the tank needs to step up and figure out what he's doing wrong.

Second boss. Has a very nasty ability with a long cast time that will one-shot a tank (or nearly) if you don't run out of the purple circle on the ground. Warrior tank dies on the first blast, probably because he didn't know this. I switch over to bear form, notice the nasty purple on the ground and barely avoid getting hit by the 2nd blast. There's not much time to run out on this boss, if you delay a second you're a dead bear. I manage to survive all but the last one - then die, but the remaining folks finish off the last sliver of health.

At this point the warrior says "no good" and I get stuck tanking the rest of the instance. Yay? Ugh. Bear not know instance, bear not happy, but grins and bears it.

First few pulls are crazy with my health dipping down to 1/4 then bouncing back up on the AoE packs. The big guys like to throw me around and I'm having trouble holding aggro, but we press on.

Third boss (the mind control boss) goes down easy. There's a flame effect that he does that you have to eat (turn the boss away from the group), but the lava cast can be stopped. Avoided the clouds on the ground, and pulled it off.

More trash. Some of this is gauntlet type where you drag everything to the gate before the last boss because it constantly respawns. Somehow we survive that.

Last boss was interesting. Once again it was basically me, the paladin healer and the mage left standing at the end.

I don't like tanking instances that I don't know well. Especially in random PuGs. But I also need to know the instances. So I might queue up tomorrow as a tank and see what happens. There's only 2 instances I can get slotted into right now, so I have a 50% chance that it will be TotT which I know have better knowledge of.