I think it would be usefull to have a user rating.

I have dld no end of movies that were either mis-titled (I had to laugh when my girlfriend tried to dld a film and ended up with porno) or just won't play because they were encoded with some wierd unknown codec.

I have no idea how it could be implemented on a P2P system. but at least users would have a guide to whats hot & what rot.
+ the spammers would have to work a bit harder to screw up the ratings and not just leave it to an automated system.