Zelig, the appeal of facebook is best understood from the perspective of lazy people like me who are incredibly popular and couldn't possibly be bothered to manage everyone's contact info in some sort of a dynamic contact management system.
You'd be surprised how many people you know and what sorts of interesting things they are up to (travelling to places, taking pictures, getting married, getting divorced, eating a pie)
Facebook is kind of like going for a virtual walk, but the only people you run into are people that you already know, in some way.
"Hey, that's my friend's neighbour's sister, who I briefly talked to at that party 6 years ago. I wonder what she's doing in Mongolia."