I have always thought that Facebook's success was tied to their targeting of the next generation of consumers, that is college students, who had not yet made a brand or technology commitment.

In this way, they gather together a core group of users who in turn draw marketshare away from others both within and outside of their generational cohort.

In my family, it certainly worked that way with my sister pulling my mother, father, and eventually myself into using Facebook as the primary way to share family information.