nerds: self-identify!
I'm always intrigued when people try to extend the way online-style communities and social networks to the real world. online communities are so fluid; something as simple as replying to someone's post or being a friend of their friend puts you in their community. joining is as simple as showing up. I just saw DSButtons.com; their tagline is "an invitation to play." basically you wear a button saying you're a nintendo ds nerd and want to play ds with random people. wearing webdesign-nerd tshirts means something similar. and then there is bookcrossing, warchalking (even though it never caught on), stickers with urls on them, the orange band for dialogue... all things trying to shorten the barriers that prevent people from talking to eachother or sharing information.
also: myspace music has been really success full at going the opposite direction. mobile phone social networking is trying desperately to be midway between.