Time to take it personally -- i.e., to pervasively use access control lists for social networking
[...] you can send text messages to individual friends or groups of friends on Pownce as well as post microblogs, or short announcements, to the larger Pownce community. This function is very similar to messaging services like Twitter or Jaiku, and is found on social networks like Facebook and MySpace (although Pownce’s messages cannot, at least for now, be sent to mobile phones). You can also send your friends links, invitations to events, or files like photos, music or videos. Of course, you can already do that on a multitude of file-sharing Web sites. It is the combination of private messaging and file-sharing that makes Pownce so novel.