I am wildly speculating here but maybe all the friends are in the Facebook. All of them. Now they also know that if they leave FB, they are cut of from information about cool parties, because as it seems, nobody cares about people not in FB. So they are all kind of locked in.<p>The situation of course is already familiar in the business world and many companies try to mitigate this kind of risks by supporting open source for example, or open standards.