The groups haven't been groups but a crowd of solo toons.
As a matter of fact, this reminds me of the posts in the Matticus' blog about breaking into raiding and how to find a raiding guild in that sense that in both of them (or their comments) its recommended that you solo up as fast as possible and start PUGging only at the level cap. I remembered this advice at the instances I grouped for lower level dungeons and found out how single minded the others in the PUGs were. They just couldn't work as a team or for the team, instead they played like they were soloing: making their own pulls, breaking the tank aggro, taking adds both by accident and by choice... and it became clear to me that the grouping should start earlier to learn at least to play the class in group.
Like Hudson and Tobold report, the selfishness is pretty concentrated on certain classes. Well, especially Hudson puts it nicely by labelling them as "Huntards" and "Retardins", which I agree completely.
Here are some advices to these classes... no, make it advice to all who are starting to group in WoW after levelling to some dungeon levels.
1) Like it says in the loading screen info: a little politeness goes a long way. You have to remember you are not soloing, but are working for the group to kill the boss of the dungeon. If you don't know the dungeon, admit it. If you start bragging about your level capped toons instead of taking into account the fact that you don't know this particular dungeon and you act like a douche bag, you are not a team player. And not invited easily again.
2) In dungeons and instances, it's always the group first, own toon second. It's like playing american football: you do everything in your power to ensure that the quarteback can deliver. It's the same in the dungeon. Which leads to
3) Know your role in the group. Tank IS tank, DPS is DPS and healer is -quite surprisingly- healing. DPS, even if he's the best geared of them all, is not taking the aggro from the tank and expect to be healed. Never.
4) Know who and what is the most important in your group. There is one simple rhyme to remember:
#1 If tank dies, the group dies.
#2 If healer dies, the tank dies.
#3 Return to #1.
5) If unsure of your position, take care of the healer. S/he'll thank you later.
6) Keep track of your aggro. Get Omen or some sort of threat meter. Now. And learn to use and read it. Really. Especially if you're playing Hunter.
I must have left so much out, but that covers mostly what got stuck in my mind during a few successful and disastrous lower level dungeon runs. The worst had it all, starting from a player with several lv70's and later admitting he didn't know ZF at all (his first visit, but he acted like he owned the place. Well, ZF pwnd him. And the group.).
I hope this helps. In fact, I think I copy this to our guild forum.
Hell yea, recycling!