From what I've read, there are a lot of quitters and teamers. This has been a problem for quite a while and isnt likely to change. I played MP after release and had some mixed experiences- some good, friendly games and a few not-so good ones ruined by typical, all-too-common d-bag griefers.
My GF and I play this game all the time, but only against the AI. If you also enjoy playing the AI, get the Generals expansion for more opponents; it's well worth the 200 points, imo. (I wish they'd release another.)
Can YOU
Escape from the Dead?