Heres a quick primer to catch you up.
Welcome to cataclysm tanking! Currently avoidance is king. Block has been majorly change, currently a 'block' will only absorb 30% of a hit, and a critical block will absorb 60%.
Mastery for a prot tank gives you a greater chance to block. Your goal as a tank in cataclysm is simply to become 'unhittable' which is better prased as 'Full combat table coverage' aka when an attack from a boss hits you it will be dodged, parried, or block. Only right about now are warrior's starting to reach 'unhittable' with H t12 loot.
Basically you want to stack stats like dodge, parry, mastery. Threat stats are gone and dead, recently threat was hotfixed to be 500%, extra bonus. Its stupid, even fury warriors getting tricks of the trade, blowing every cooldown with portion and blood lust won't pull off of a decent tank.
So as a warrior you want to stack parry dodge about even, slightly more parry to favor procing hold the line. Then you just stack mastery, more mastery the better.
[Today 06:48 PM] Ion:swimming in a natural body of water ISN'T acceptable...it's momentarily tolerable