I use Facebook to keep up with some out-of-town friends and relatives whom I wouldn't have much contact with otherwise. Also with a few people I've met online -- here, on another board, or on FB itself. By now I've unfriended all the old school friends. After the initial catch-up, we had nothing to say to each other. I also find FB pages to be a convenient way to keep up w/ local news and events.
So it's become much more important to me than I'd expected. During that almost two years that I was pretty much homebound, it was a real lifeline. Now I have to get out of the habit of spending so much time there and online in general!