Is there some principle that states that the value of a social network is the square of the user base? Some networks have a business model predicated on keeping their head count limited.
http://news.ycombinator.com/item?id=1319054
The idea is that a network is more valuable the more connections there are in the network. Think of the difference between two new people added to the end of a line connected front to back, and two new people added by connecting them to everyone already there, who are also connected all to each other. The latter is more like a social network than the former.