I'm testing Prot Paladin in the Beta now to make an informed choice between Pally/Monk/Warrior tank when live hits. Now, I know Monk's active mitigation is through 1) Judicious use of Guard, 2) Keeping BoK up for Shuffle, and 3) Knowing when to use Purifying Brew to clear Stagger. Prot Warrior's is through knowing how to manage Shield Block/Barrier.
What is the Paladin's? As I near as I can tell Prot Pallys are roughly back to Cata launch where you get your damage reduction via using Shield of the Righteous, which is a staple ability. There doesn't seem to be (and keep in mind I've only very very VERY briefly tried it out) any real "choice" to make since without using SotR you're taking unmitigated hits. Sure, you might occasionally use WoG but it seems very passive compared to at least Monk/Warrior.
I'm not saying that's necessarily BAD, just trying to get more informed since the last time I played my Paladin seriously was in 4.1 with the great WoG nerf but they seem to be a solid choice going forward into Mists (and Ret feels a lot more interesting than Arms/Fury atm).