I think the problem is the attitude that other people take towards it - like it's play money, so they don't play like they would if it's real money. Take about an hour of your time and play the play money tables at Party or somewhere. You see the screwiest plays ever. People throw all their money in every hand and just rebuy when they run out and stuff like that. I played play money for a while and I'm pretty sure it screwed me up at first when I started playing real money because I figured it was practice for playing with real money. Bad assumption on my part. People's motivation changes when it's for real and so does their play.

OTOH if you are aware of this and are just out having a good time, then it shouldn't screw you up any more than playing Omaha screws up your Hold'em play. They are both poker, but they are still very different games.