I have main-tanked all of SSC, except for Tidewalker, where I do the murlocs. Personally, I think Tidewalker might be easier for a pally tank. We would probably take fewer crushes than a warrior, and he hits fast enough that reactive threat would be high. In addition, our threat generation is less dependent on attack speed than a warrior, so the debuff wouldn't hurt us quite so much.
Hydross, you can tank one of his phases and a couple adds. In theory, one pally could tank him and all 4 adds for a phase.
For Leo, I've tanked the human phase, and having avenger's shield is great for grabbing agro after a whirlwind. Recently, though, I've gotten a fire resist set (350 FR), and I tank his demon phase. With enough spell damage, you can grab very fast agro with exorcism/avenger shield. It's also a huge benefit to be able to drop a de-buff stack whenever you need to using divine shield (usually right before transition to phase 3). Just make sure to get hit by his whirlwind a couple times during human phase, so you can regen your mana. We've had much smoother kills this way, than we ever did with warlock tanks.
I always tank Karathress, as we have our warrior on the priest add, for additional interrupt. We've had other pally tanks on the shaman and hunter adds, so all are doable.
We recently got our first Vashj kill, and I main-tanked that as well. We had two pally tanks. Probably not ideal, since it'd be nice to have some sort of charge. Phase 2 is fun. I would grab the Naga elites and bring them to the other tank who would taunt off me. That left me free to roam about and stun striders when they appeared. It's also really useful to have an extra cleanse for the poisons tossed about when tainted elementals spawn (takes a little burden off the healers).
Other than that, we've only downed Solarian (pally's are great for the adds) and VR in TK. We haven't even attempted Al'ar yet (wanted to down Vashj first), so that's coming this week.
We also spent one night in Hyjal, so we've only got Rage down. Obviously, Pally tanks are awesome for the Hyjal trash, but I tanked Rage as well.
In any event, you should be capable of main-tanking almost anything in SSC/TK. From what I understand, there are some fights later on that are trouble for pally tanks because of silences/mana use. But, I'm looking forward to either figuring out a way to do them, or throwing on my healing set for that.