Found an interesting piece on Wired.Com about a new music service, Guitarati. What makes it different from other music services is the why music is categorized. Each song is assigned a color based on the mood of the song. It is some sort of mood ring for music. The system is still in Beta, so its popularity or success has yet to be determined. However it is an interesting concept. You can read a review of the Guitarti here.
If you decide to give Guitarti a try let me know what you think about it.