I used to think about Facebook the same way you do, but then I got into competitive card gaming. The local community for my game of choice is organized entirely via Facebook. We organize tournaments, carpooling, and so on, and invite each other to related social events.

It's a really nice way to handle a loose network of acquaintances like this. You don't have to give out your phone number, you get Event pages, it's pretty resistant to Spam, etc.