Monks have to be played perfectly right now, purify often and never drop shuffle are just the basics, guard has 2 charges so I'm more liberal in its use and it helps a fuckton.
In heroics I have little problems, some pulls here and there, but nothing spectacularly hard, providing that everyone knows what to do.
The rest is based on a collection of tricks, for example if you play a brewmaster, remember one thing: if you ae stun a lot of mobs, their swing timers reset, so you should not stay there like a tool when the stun wears off or you'll be (almost) instagibbed. Generally speaking I'm having a good time tanking as a monk, I do also a truckload of dps which never hurts (I love chi explosion). I also use and abuse the new Ox Statue functionality: it's an agro magnet, it's almost an AE cc and it's incredibly good when grabbings spawning adds (they hurt *nobody*, not even you for a good while). Gotta be careful in placing it down when pulling, because it has a huge range. As an added bonus, if a mob is CC'ed long enough, the statue will keep building threat: had a mob in Skyreach that after a 1 minute CC, was beaten to a pulp and he never turned on anyone in the group because he was sooo mad at the statue that it was almost comical.
Anyway it's active mitigation, not passive, so the best players will be the best tanks, gear being equal of course. As I said I like to CC because in the end with my current gear I cannot AE tank everything all the time, so I prefer a 2 minutes longer run than wiping.
You have to consider that if everybody is doing 6k dps, there is no good tank that can take punishment forever, sooner or later it's going down.
EDIT: I got Croman the Barbarian yesterday, hah!