Recently I passed by a girl in about 25 years old and I had heard her saying: "I don't like meeting my old friends, because there's nothing to talk about! They know everything from Facebook!".
After that, I started wondering why is Facebook or some others social networks so important to us. Sure, we like to keep abreast of all what is happening with our friends, family (or even people who we don't know much, but still - they're our "friends" on Facebook) but isn't it better to meet those guys and talk to them on-live, not on-line?
Personally, I don't use any social network at all. I think it is better to have a few real friends instead of houndreds of fake ones.
Thing that matters number 1: real friends and contact with people.