the art of being critical on the web

Something that Rafe said the other day really struck me, because it’s a problem I’ve struggled with in the past: how do you provide unsolicited feedback on something when you know there’s a good chance that your criticism could offend a friend? Generally speaking, I’m all too happy to hear people bitching about things I’m responsible for, and I think I’m fairly good about accepting the comments at face value. My experience suggests that I might not be totally typical, however. (Shocker.) How do people handle this?