It seems like it is very easy to tank over your head in the new expansion. At 72 last night I tanked Drak'Thar or whatever that troll instance is called. Most of the mobs were level 76. I also had a level 70 healer healing me who was falling asleep at her keyboard.
I did get a few nice things out of the instance (altough no new gear). I got two cooking recipes (including one for cupcakes....nom nom nom) and I got the recipe to make heavy frost weave bandages. I love being able to tank things that are very high above my level. It gives a sense of accomplishment.
Hopefully this weekend, I can do the Old Kingdon and get that instance out of the way. I picked up a level 73 BOE blue shield off of the AH that will be replacing my Merc Gladiators Shield Wall.