I feel like this has been hashed out a million times on HN. Yes, e-mail works. I could e-mail a photo album to people. But what if they want to comment on it? Either everyone gets spammed with hundreds of e-mails, or there's no group conversation. Add to that, being tagged in other people's albums. Facebook provides value to people. Not all people, but that's the way the world works.

And of course there is a value in passive communication. I want to see the photos my friend posted of his holiday. I don't want to have to look at them right now, though- I'm busy. So I'll look later. Ta-da: passive communication.