It's all about optimizing recommendations. If you just have a star or not starred. There's a chance the service will recommend a song you will likely hate (now you could be clever here and factor in skips). So now we have Hate, Love, Unrated. This works except for your OCD users will want to rate everything. And the more ratings you have, the better your recommendations will be.

What about Hate, Like, Love and unrated?

I always liked the idea of being able to specifically call out those few liked tracks that are a just a little more special :)

I only use one, three, and five stars, and it determines the "mood" of the song. One star songs are slow and chill, Three star songs are upbeat, and five star songs you'll want to rock out to.

Couldn't that be accomplished using BPM? Various tools will determine BPM for you.

Agree. Binary on/off with the stars is a lot easier to keep track of than remembering how you define each of the 1-5 star ratings.

All told, I think rating songs in your library is a really personal thing.

@JimEngland, you use stars purely as an organizational tool, which is slick. It's cool that the iTunes interface extends it self to different uses.

@tkahnoski and @zeedog, how would you elegantly expose controls for those different feelings?