Best way to treat pingbacks?

Can anybody tell me if I should approve friendly and relevent pingback comments? Are they good for SEO purposes or something? I mean, if you have a real conversation going on in comments and then there’s this nonsensical (but otherwise positive) excerpt tossed in, what does that add to anyones life?

On the other hand, someone is connecting their site with mine and that seems like a good thing that I don’t want to chop off by deleting the pingback.

Anyone have any knowledge of their role and value?