You'd be surprised how many people you know after 50 years of life...you'd also be surprised how many of them are on Facebook.

Granted, a lot of those people aren't close friends or family members. Many of them are people that my parents knew decades ago and have lost touch with. I actually think that one of the most valuable things about Facebook (and twitter) is that it allows you to more effortlessly keep in touch with more people than 1-to-1 communication methods like email, phone, IM, etc.