iTunes recently added a feature that lets users group multi-movement works together, which is especially useful for those of us with Classical music. Specifically, I love it for Baroque music, so that I don't hear some random, thirty-second-something middle movement out of context of the much more developed sections:
http://www.kirkville.com/apple-is-finally-making-itunes-better-for-classical-music/
It would be great if Subsonic could do this, too, as it is my default music player--I only use iTunes to sync the music on my various iDevices.