FNM was one of the "rock" groups that I really got into. I especially liked Angel Dust and the King for a Day albums. Billy plays an important part in creating the FNM sound. His presence is definitely felt. In some songs he even sounded really cool just riffing away with a pick! And I don't say something like that too often!
He's done much more then slapping in e (those were basically two songs in the same fashion: epic and we care a lot) Check him out on the song King for a Day, were he plays the fretless in an agressive song. Check out the line from "Evidence" for sheer perfectness, but above all: Listen to the interplay with the drummer, that's were it really gets interesting. It just doesn't get any tighter than that! (for the sake of generalising, there's probably a band who does it better, but in my small world of perception...)
oh i know hes done much better then just slap an open e. He is becoming more and more one of my favorite bass players. And yes, the rythym section of faith no more is one of the tightest in any rock/metal band EVER. Maybe thats why they were the only two that actually remained in the line up from beginning to end.