My mage is far too eager to "take one for the team", she is a good 10% xp behind the rest of the group because she dies so often. She's also arcane spec, so it's not like she's getting aoe threat. She is also a bit of a slacker and most of the time if I'm fighting and one toon is doing nothing it will be my mage, who dropped follow a little while ago, usually anywhere there's a patrol or respawns. She's the top dps though so I don't think I can replace her :P

My healer likes to get stuck behind things, but she's a gnome so I can't blame her too much. Haven't done COT Dark Portal yet, but they fixed the water there I think...

My warlock likes to chill at the bottom of the dps meter and fail to soulstone anyone (I really should sort my macro for that out), occasionally she'll send her pet into the wrong group just to make things more interesting.

I also struggle sometimes to assign loot on an objective (who needs it more, who will make the best use of it) basis and find myself thinking about whether the toon deserved it for that fight or not. Probably my own fault for running with 3 clothies.