I've cleared almost all heroics (only occulus and halls of stone left), naxx, os and voa while multiboxing a prot warrior tank. I've got one castsequence on the warrior that spams thunderclap, demo shout and devastate. Tactics are slightly different from the palladin tactics (instead of placing down a consecration, you place your warrior at that spot and the spam macro should pickup the adds).

There's only two boss fights that I've encountered in northrend that are a bit tricky with a warrior. Anub'arak in Azjol-nerub takes some practice because the adds that spawn during the fight will tend to directly go for your healer (not really a problem if you're prepared to taunt them immediately). The tribunal of ages is really a pain because the adds in that fight are scripted to run past your tank and attack Brann instead, although I have to admit I've only attempted this fight a couple of times.

A prot warrior (only) adds a health buff to the group. It does make a big difference when you're starting with heroics, but it becomes less useful once your gear becomes better because you only need sufficient health to survive an encounter (any extra health only serves as a buffer). What does make a big difference are the warrior's damage reduction debuffs. Stunning entire groups of trash, disarming whirlwinding bosses and reflecting spells does contribute to the survivability of a group.