I better prefer a person that perform awfully but actually try and learn from his/her mistakes in my group rather than dude that stare at dps meter and whine. I have beaten many battles/dungeons with members that started to get better during the fight when they asked questions after wipes or other party members just adapted to less experienced members' play style. Also dps must have a bit of brain to slow down his damage sometimes, to attack the right mob etc - not just smash something as hard as possible.
But every time I hear "dps is too low" I know that 1 dude just killed mood for everybody and "dc" or vote to abandon will follow soon.

P.S.
I often notice that bigger whiners are i90+ geared players that completely suck themselves so they choose another player in group that seemingly has the lowest ilevel and use him/her as scapegoat for inability to clear the raid or dungeon. In lot of these situations scapegoat actually perform much better than the whining weiner.