I read a very good article on WoW Insider this morning, called:
Shifting Perspectives: Tanks, "Wrath," and crushing blows
I strongly encourage everyone to read it, that will give you a very good insight into one of the main problems of current tanking in WotLK ... in fact, the removal of crushing blows was a bad move.
I'll write a short sum-up of the very good article by Allison Robert, which despite being aimed at druids tanks covers the depth of the problem very well.
Crushing blows were 15% of the hits of any mob 3 levels more than you (hence raid bosses) that will hit you for 150% of the damage. Crushing blows were only affecting physical blows and never magical ones.
The 3 classic tanking classes dealt with them differently. Warriors and paladins with block/dodge/miss/parry were able to "remove" the crushing blows from the hit table (by achieving the famous 102% of total avoidance). Druids were not able to do that, so they just ate the crush with more armor and health pool.
Now Death Knights were added ... tanking without a shield, and with plate armor and a lot of abilities. They could not have the health pool of druids, so Blizzard decided to remove the crushing blows from the game to allow for the DK to tank. OK ...
And now look at the damage of WotLK: no physical crush, no physical big burst, the real hard points of tanking right now are magical bursts on Sartharion (+drakes) and Malygos.
Druids are still able to compete with DKs for tanking, but warriors and even less paladins are not. Block is a nearly useless ability in raid content right now, but for trash aoe tanking. And a tank that will only see trash tanking night after night, when he was promised "tanking equality" will not be having fun in this game.
Warrior tanks are rerolling, Paladin tanks are respecing healing (if they respeced to ret they will ahve to change in 3.1, ret being finally "nerfed to the ground" in that patch thx Ghostcrawler, all paladins love you dearly for that). Don't be surprised if the tank shortage went even worse than before LK ...