David Weinberger says: if you want to get at the real social networks, you're going to have to figure them out from the paths that actual feet have worn into the actual social carpet.'
So right. The best examples we have today are things likeTechnorati and the Blogstreet neighborhood and All Consuming that
Here's another way of looking at things. The Social Network tools are about saying hello. Unless you're 18 months old, hello is only .1% of the conversation. Weblogs, wikis, and other public conversations are about the other 99.9% of the conversation. And the Technorati/Blogstreet/AllConsuming applications help you find relevant conversations to join.