"White Label" Social Networking Sites
A few days ago, I had listed 3 platforms (Flix, Ning and KickApps) that allow you to build your own social networks. Well, the market is very crowded. Here is blog post from Jeremiah Owyang that has a much more comprehensive list.
Low startup costs have filled every corner of the social web software with hundreds of players. It will be interesting to see how it all shakes out. I guess a large volume of small amounts will be lost!