I almost want a PS3 just so I can see the glory that is "Little Big Dick Planet" 2 hours after launch.
There's an interview at a trade show with Kyle Shubel, one of the devs, who admits that penises are going to be a problem. It's in the hopper now by the way.
LBP has pretty simple community moderation. If you see something objectionable you just press Select and it pops up a griefing report screen, which then gets reviewed by someone.
I don't know what the disincentive is though. Even if your PSN account gets banned I don't know how they'd prevent you from just setting up a new one (although if you start having to juggle multiple accounts to deal with DLC it might get frustrating and possibly expensive for the griefers).