I'm not sure what it's good for yet. It seems to support conversations (in comments) better than I'd expect, so that's nice. I dislike the way it does links. Just let me put in my <a href>s, sheesh. None of this picture & excerpt nonsense.
I suppose I can send out invitations if you need one, although it doesn't sound like they're hard to come by. My understanding is that they're throttling entrances by having invitations work only sometimes, so if you already have one but it didn't work, try again later.