See, that’s what I would have thought about StudiVZ and yet Facebook could spread in Germany like a wildfire. StudiVZ still has millions of users but Facebook has those same users, too. (This is only anecdotal evidence but Facebook also seems like the busier place to me, activity has transitioned from StudiVZ to Facebook.)

This tells me that even if a social network seems to have a particular market cornered, a competitor still has a chance. (Which, I think, is quite nice to know.) Network effects are obviously important and have to be considered by anyone who wants to build a social network but I think there are certain properties of social networks that dampen network effects: Signing up is easy and free, for one, and rebuilding the social graph, while some work, is far from tedious. You only have to add some friends and recommendations get you the rest of the way.