It's the applications that are interesting, not the infrastructure. And Orcut, Friendster, and Tribe.net are all just infrastructure. They're big databases full of relationships, but very little else. On top of that, the standards are all in place. It's as if these big repositories of data are being handed free APIs: FOAF, iCal, vCard, et al.
The interesting thing is that the social network sites own the contract between you and your so-called-friends.Jeffrey Veen: Will you be my friend?
Excellent write-up. It absolutely is all about the apps, and there are a bunch of open APIs already available. There is nothing wrong with being infrastructure, but that infrastructure needs to be open, extensible, and not barricade your own data. Ideally, federated identity and personal profiles will allow you to link between many different systems. Each system will be better than another for certain functions, regions, interests, etc.
I'm hoping that Drupal (that already federates identity) will go one step further and actually share profile data between sites as well. Then, anyone will be able to create their own social networking site. Or use Flickr: it's still on my Cool Network That Isn't Evil list.