>I strongly disagree especially in the case of social networks. First movers in such spaces have incredible advantages and one of them is a lock-in effect. Countless follow-up social sites have come and gone that either had feature parity or better offerings than Facebook, but failed to get a foothold because of the fact that everyone already had Facebook. Why switch when everyone can already talk and plan?

Sure, and that applied to Friendster and Myspace and others as well, until Facebook came along.