The reason Facebook became so popular, initially, was its exclusivity. I remember being on campus when it first became big -- and at first it was an Ivy League social network created out of Harvard, and it created a sense of exclusivity among its members that sites like Friendster never had. A lot of people I knew were disgusted when it was released to the "state schools", because it diluted the value of their membership. The state schoolers then became upset when it was released to high schoolers, and so on.