Dave is right on this one. There is something inherently wrong with the categorization of people: We are complex atoms, moving. Categorization is something simple and static.
When I tried to create lists with circlehack.com I immediately stopped over the obvious one, family. It’s already complicated for this one. I’m connected to so many different people I just can’t categorize them all, at all. Also I feel awkward to arbitrarily say "you, you’re into tech and that’s how we met" because it might not be the essence of our relationship right now. And what will it be in three years? Should I keep a constant look at my lists to match the present? Waste of time (not for Google or Facebook, obviously).
Categorizing people means that you assume you are the one knowing what they like. But maybe they like to read stuff from you because they like you and trust you so they read it. Otherwise they would not read something about this subject because they don’t care "that" much. But because it’s from you, they do. And you don’t know what interests who, it’s probably changing all the time. It’s organic. It can’t be processed with lists or circles. It can’t be processed efficiently with the help of algorithms (not yet at least and I think for a very long time).
I now understand more why Facebook never really got into this filtering, it’s not very human and overly complicated. As a user I’m glad I can just drop an article for everyone, to read. I think it’s richer this way. It’s good that my little cousin can read something about the war on drugs even if he doesn’t give a shit right now. Following him is interesting for me too. More knowledge, more change. As long as I can block some content if I want to –Foursquare’s check-ins-, I’m good. Less headaches (shit, is this dude still in this list I want to share this drunk picture to?).
Whatever happens to social networks, there will never be one and only one. What is more useful to me is how we can automate how we push our content and to what networks we share things.
I think services like ifttt have a great future.