I like the idea of using stars to indicate favorite tracks. iTunes has a 5 star rating system that I use to keep my music organized and I wish Rdio had the same.
@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?
I always liked the idea of being able to specifically call out those few liked tracks that are a just a little more special :)