Also, as mentioned, Facebook (or Google+) is an unique way to stay in touch with people you don't see no more. It would be totally impossible to communicate daily with 100 people, but with Facebook you can just skim through the flow of information effortlessly. I mean, you wouldn't send e-mail to one hundred people you know to tell you just had a funny encounter. But you can write that kind of stuff in Facebook, and people who find it interesting can react to it. Others will just skip it.