Warren Ellis does some thinking out loud regarding social networks and micro-blogging:
So, are people rolling their own private microblogging networks yet? And knocking together mobile pages and writing/hacking desktop apps to work with their private microblogging networks yet? It would seem to me to be the obvious outgrowth of the Twitter phenomenon: ambient communication for secret societies.
I would love to have a private Twitter network for just my friends. Apps like TweetDeck serve to compartmentalize tweets, but not to compartmentalize the whole network.