Friendster - currently in a free beta period, although they'll start charging for some aspect(s) of it sooner or later - is a rather interesting site. Rather than creating yet another dating site designed to help one meet total strangers, they've designed yet another "six degrees of separation" (well, technically, it's only four degrees, but that's plenty!) site.
So what's interesting about it? Well... I know who my friends are already. But I don't necessarily know who their other friends are, or who those friends' friends are, or who those friends' friends are. Nor do I know whether there are people among all those friends who might have interests in common with me, live in my town, or whatever. Or rather, I didn't know. Now I do.
It's also interesting to find out that a friend I've made recently knows someone, who knows someone else, who knows a friend I'd lost track of years ago. It's interesting to find that I'm only a couple friends away from someone my daughter's mom went to high school with (hundreds of miles from where I went to high school). And it's interesting to find cases where three different friends of mine know different people, who know different people, who know another individual.
Anyway, if you're a friend of mine and not on there yet... feel free to look me up.