I don't know. I avoided myspace like the plague but facebook is a tad less tacky in many respects and it has actually helped me to catch up with a LOT of old friends from college, high school, and even further back. It's even saved me money as I discovered an old friend that lives in town and now she picks up my oldest from school 3 days a week and keeps her until the wife or I can get home.
Certainly, you can do childish things with Facebook but most folks who use it that are my age and older just use it to reconnect. Of course, if you don't want to let people know what you've been doing since you last saw them, that's another thing....