Here in Netherlands, before Facebook, we had a social network called Hyves. One of the reasons it failed is because of the disassociated graph, like you mention

Here in Netherlands, before Facebook, we had a social network called Hyves. One of the reasons it failed is because of the disassociated graph, like you mentioned. You start out with all of your friends from high school, but once you start to grow.. the distance between you and them growths. That is why people started moving to Facebook, because all their cool friends where there. I guess the only reason why Facebook is still surviving is because everyone is on there, you do not want to lose certain friends. They have conquered the market.