Joe LaPenna offers a great point
about proprietary Social Networking sites like Friendster, MySpace, and Orkut. These networks do not compete on technical merit, only on size of their audience, as that has a direct effect on more people signing up with their service.
I don't totally agree there, I think MySpace has taken away users from Friendster by offering more features like digital media and games (no solid numbers, just a hunch of mine. I wonder if there is anyone tracking these numbers). But that being said, Joe is right, it's stupid that there are multiple SN's out there. What's happening with FOAF? Unless Freindster or MySpace allow for Open API's like Joe suggests, if an open SN tool comes along, they'll all be toast.
Dating and Business Contacts are still the 2 most popular applications for SN at this point. So as long as Social Networking is being used for Social Networking, we'll have this problem. What we need to see is SN being used for something else. Any suggestions?