I was annoyed at the sheer length of time it took to receive a formal invitation. They built up hype way too early. By the time it was available I didn't really care anymore, I had moved on to other things out of frustration. How are you supposed to successfully launch a site in which you interact with friends but not let anyone in (at a decent rate)?
I think the last time I looked at it, it required an invite. I didn't care enough to give them an email address. Or maybe it was the same as now: the front page has "login in with Facebook" and "log in with Twitter" as the only actions. I don't want to do either of those things. Just play me some music, then if I like it we'll talk about logins. Pandora got that right years ago.
