I said Twitter, but really I'd probably say blogging if that were an option. I have a kind of blog community, of people who comment on mine and mine on theirs, are they are probably my closest online friends. But most of them I also know on Twitter, so that's why I picked that.
Personally, I have an aversion to Facebook that I am trying to get over - just don't like all the people from your past contacting you, and feeling like you have to befriend them, etc. I prefer sites like StumbleUpon that are more content oriented, or Twitter, that are more freewheeling.
