After waiting almost half an hour to get into a low level dungeon for my roulette as a MCH I had the displeasure of immediately seeing the tank take his leave because he 'didn't like the dungeon'. I find that sort of attitude horrible since it screws over three other players  - two of which are DPS and will no doubt be stuck waiting around for a new tank to arrive...or they'll just have to leave themselves and queue again.
