facebook isn't worth shit.
just as myspace destroyed friendster, and just as facebook is destroying myspace, someone will destroy facebook.
facebook has a lot of users but the most active ones are 17-30 year olds. remember, it started out as a college social networking site. people in this age group are interested in "the next cool thing", and facebook is cooler than myspace. myspace got old and tired that's why people abandoned it.
one day something more fashionable than facebook will come along and the process will repeat. these sites are like jeans -- in style one season, out of style the next.