Cory Doctorow has written an article for InformationWeek entitled "How Your Creepy Ex-Co-Workers Will Kill Facebook". The main point of the article seems to be that these 'social' sites that encourage us to make a list of all of our friends run into trouble because it's awkward when someone you don't like wants you to add them to your list.
It's a valid concern, although this isn't a problem that's presented itself to me thus far. I don't know of any easy way to solve it: we could all just let anyone know what we're doing, and save the really private information for personal correspondence, but that removes some of the benefit of automation; we could tell people when we don't like them, but that would probably cause some trouble, too.
Honestly, I can't bring myself to be too troubled by this. Perhaps it's because I'm antisocial: I have a facebook account, and my friends list has two entries. I don't remember the last time I logged in, but I guess it's been a month or two. If facebook manages to solve the creepy-co-worker problem, more power to them. I'm still waiting for a brain implant to show scores over peoples' heads so I can rely on that rather than remembering who my friends are.