If you find the new iTunes 9 feature "Home Sharing" a bit lacking then you may be interested in this remote management compendium I put together a few months ago. If you're ready to really get your hands dirty with things like ssh, rsync, launchd, and more, you can design a system to copy/backup/add any iTunes files to other iTunes apps on your network in the background.
I've added a Part 5 to DIY: Remote Management Assortment that describes how to create and delete playlists on a remote user's iTunes with ssh and osascript. If you haven't been following along in this series of projects, you may want to start at the beginning; this newest addition builds on routines and concepts from earlier in the series.
DIY: Remote Management Assortment is a tutorial suggesting several methods of manipulating iTunes files among users on a network, with particular emphasis on using AppleScript to swing passwordless ssh, rsync, scp, osascript, and other utilities. Rather than develop a batch of scripts for you to download (and have to support), you can use the fundamentals described here as the basis for your own AppleScript projects.
This tip at Mac OS X Hints, Make sure iTunes mounts a networked music library, provides a simple method to ensure that the network drive containing your iTunes Music folder is mounted when starting iTunes. Simply put an alias of the iTunes app on the networked drive, copy that alias to your Dock, and launch iTunes with that.
I've updated Remote Management Scripts, which is a collection of scripts that assist with managing/editing/copying shared tracks on a remote machine via the iTunes on a local machine. Nothing too major: I consolidated and streamlined some routines, changed the loginLib.scpt to allow the iTunes Music Library volumes for each machine to be listed (rather than in the individual scripts that require them), and provided an option to unmount volumes after scripts that mounted them have finished.
Remote Management Scripts have been up for awhile and enable you to manipulate tracks/files from a "Shared" music library--providing you have access to the "Shared" computer (username, password, Bonjour/Rendevous name, and the drive that the music files are located on). I was using them today to move stuff around our home network. Seems to me I can make these easier to configure and use.