1) It’s asymmetrical. (I think that’s the right word.) You can follow (and unfollow) whoever you like. The people you follow don’t need to pay any attention to you and vice versa. That’s the fundamental difference between Facebook connections and Twitter connections (w/ regard to people, not Facebook pages). Not better, necessarily, just a fundamental difference.

2) For most people, the value of Twitter isn’t what you put into it, it’s what you pull out – the listening aspect. I manage lists of some of my favorite designers, planners/strategists, typographers, nerds, etc – people who find and tweet about the coolest stuff they find – most who I wouldn’t/couldn’t be friends with on Facebook. So it’s an easy way to filter the web for awesomeness from your POV – and share/re-share if you want. But you don’t need followers. You just need to follow well.

3) It’s a great example of a simple, open system (API) producing a really complex, sophisticated network of relationships, information, apps, etc. And it only gets richer, more interesting as time goes by.