*Warning: Incoming rant*
My druid is now level 63, and got from 60 to there without doing any quests, just queueing up as a healer in the Dungeon Finder. Overall that worked not so bad, because while we remember the terribad pickup groups more, and discuss them more, there are actually more than half of pickup groups which are competent enough for the content the Dungeon Finder assigns them to.
But in those pickup groups I've been in that went pear-shaped, the tank was invariably a death knight. Usually a death knight with absolutely no defense gear, low stamina, and in some cases even somebody who had to be reminded to switch to frost presence. In two groups yesterday the dps warrior of similar level had *more* health than the DK tank.
With low health, low defense, and no shield, a death knight tank can go from full health to dead while having a full set of heals over time on him in less than the time it takes to cast a healing touch. Even more annoyingly I experienced several wipes where the DK tank had overpulled, I barely managed to keep him alive at the cost of all my mana, and then we wiped because the tank had ignored my "out of mana" announcement and went and pulled another three packs of mobs. And then of course everybody blames the healer and leaves the group.
Dear Death Knight: At this level you inherently suck at tanking. You don't even *want* to tank, you just signed up as tank because it meant less waiting time in the Dungeon Finder queue. So please, could you at least pull carefully and watch the healer's mana between fights? Once the healer runs out of mana, you are dead.