Here is something I wish the iPod could incorporate into its next software update -- some way of just auto-categorizing my music by moods. It has something like that based on the Rating system, but its too unidirectional for me. For example, I don't feel like listening to all my 4-star songs one after the other every time I want to hear my favs. Well, give this a spin and you'll know what I mean.
Musicovery : interactive webRadio