Faceook should be an option, not a requirement!
The forced (and I emphasize forced) integration into Facebook is a bad idea. If people want to login with Facebook, or willingly want to share their music, that is fine. I do not have a Facebook account because I do not want one, and I should not be forced to have one simply to listen to online music.
Facebook has dubious privacy practises, and they are under investigation in several European Union countries for privacy violations. Here in the US, they have been accused of tracking members (and sometimes non-members) even when they are NOT logged into Facebook.
Facebook also has the nasty habit of forcing you to share things by default, and the service makes it extremely difficult to keep things private. I have it on good authority from a Spotify user (who incidentally has Facebook) that the Spotify settings keep resetting themselves to the "share my music with my friends" mode if you are not careful.
The argument used by Spotify runs something along the lines of "think of it as whole new world of music sharing," etc... If I want to share my music, I will do so. As I stated earlier, Facebook intergration is there, but it should be only for those that want it.
In my humble opinion, this is a poor business decision, and Spotify is alienating a large part of its potential customer base. Facebook is not the internet. AOL once was thought of as "too big to fail." Will Facebook be the new AOL?
For the record, I will stick to Pandora and Slacker for the time being.