iTunes 9: no social networking, plenty of new features, breaks Palm Pre sync
If you have more than one computer on your home network, you can now share your iTunes library with up to 5 other machines. Previously, you could view and play music from shared libraries, but now you can import songs from other authorized machines, and play your purchased music on any of them.
The Music Store
The iTunes Music Store has gotten a nice facelift, and is now a bit easier to navigate. The big news is that both music and movies now have extras. New iTunes LPs feature album artwork, liner notes, videos and more, putting a digital spin on the gatefold covers from LPs of yore (do most iTunes customers even remember vinyl?). Movies also come with extras now, which should attract a few customers who held off making the switch from DVD because of the bonus features.
When you install iTunes 9, it will re-index your library for Genius and give you 12 automatic genre-based playlists. Previously, Genius could only build playlists around a specific song, but these automagical ones turn out to be pretty good. I ended up with two pop playlists, one rap, one electronic, and one experimental, amongst others. iTunes also added a classical music Smart Playlist outside of genius, even though my library only has a handful of classical songs.
iPhone/iPod Touch Home Screens
If you're an iPhone user, this is really the killer feature in iTunes 9. You can arrange apps and organize your home screen using iTunes, save different home screens, and then sync the one you want. Moving apps around on the iPhone itself is a bit of a laborious process, and being able to drag and drop with a mouse makes it a lot easier.
UPDATE: Back to syncing for a minute. Remember how Palm managed to get around Apple's last blocking attempt? With iTunes 9, Apple has returned fire and once again broken Palm Pre syncing (according to numerous reports over at PreCentral). Your move, Palm!
UPDATE 2: Ok, so there is some social networking, but only in the Music Store. You can share tracks from iTMS to Facebook and Twitter, but there's none of the share-your-own-playlist stuff that we were expecting from the fake screenshots.