well, this depends on the area and the neighbors. Trust me, when I've done it, it's because it was serious. and the noise in question happened more than once, and was disturbing elderly people who were more upset than I could ever be. (so, in effect, I was looking out for them)
I would never call the cops on a whime. that's a waste of time and taxpayer money.
in the case of chris' neighbors, these are clearly insane people who think it's ok to get violent. and that's the reason there are police.