There are several things I like about Facebook. For one thing, I have found friends I have not seen in almost 20 years. While I backed out of MySpace right away, Facebook's privacy controls kept me around.
Besides, it lets me contact people without compromising my privacy. :-)
I like the Twitter integration and ability to post RSS feeds. I'll still Twitter, but it goes to FB as well. I'll still blog, but my FB friends can follow the summary if they want. It is a win-win for me.