I personally rsync my iTunes music library from a Mac to an Atom powered Ubuntu Server Edition Linux computer where I have Subsonic installed. It would be terrific if Subsonic could directly read and serve the playlists that were created in iTunes and save a lot of BS using applications to convert these playlists first. Along with my music there are Podcasts so syncing hourly works best and you can see how doing a lot of manipulation can be time consuming and impractical.
It's interesting to note the the Firefly Media Server can directly read iTunes playlists. I'm using svn-1586 to share across our LAN but if these same iTunes created playlists were available in iSub on the iPhone as an example how awesome would that be!