And in 5 years time, it's very possible that Facebook, like AOL, will be dominated by old people, the stubborn, and the relatively computer illiterate, as others have moved on to greener pastures.

Facebook's dominance is not set in stone. People may not be able to live without Facebook, but there's no reason they can't transition, such as how people quickly transitioned away from MySpace.

You start by having two accounts. The more interesting, cutting edge, friends are on the new network. Your high school friends, family, and tertiary relationships are on the old network. You check them both equally at first, but slowly you find yourself on the new network more often. Then, at some point, you stop updating the old one, save for the occasional "I don't use this anymore, I'm on X now." updates. Others follow suit, until at some point, the trickle becomes a flood. Next thing you know, the old network is a ghost town. Nobody cares about it anymore, and people only reference it as a relic from a distant past.

There is nothing Facebook has done to prevent this. And this will keep happening until social networking is eventually decentralized.