I was MTing in vanilla together with another tank and I don't know why any sane person would do this unless they deep down are a masochist. Sure, getting priority on Thunderfury is nice, but on the other hand you get whispers like "need tank for onyxia key", "can you tank DM i want to gear my twink for MC", "hey, you did have an UBRS key right?" and "come help plz tank ZF for my twink, the last tank ragequit at steps because we were too retarded"
I'd play feral. Needing on all the druid leather + rogue stuff and making subpar dps because I was too lazy forgot to farm crowd pummelers. Or shadow priest, using up a precious debuff slot.