Still, despite the auto-transfer limitation, this is a handy new feature that makes it much easier to ensure all your Macs have all your media.

iTunes 8 debuted , which can create a playlist based on a "seed" track. To work this magic, iTunes anonymously uploads information about all the music in your library and compares that info to other people with similar music libraries. When you create a Genius playlist, that data is used to choose a list of 25 to 100 songs in your library that other people with similar music tastes also have. In other words, iTunes creates a playlist it thinks you'll like if you like the seed track.

iTunes 9 uses that same data--data on over 54 songs, according to Apple--to create Genius Mixes. Instead of requiring you to pick a seed song to create a playlist, the Genius mix feature goes through your library and chooses tracks that "go great together."

Unlike Genius playlists, your Genius mixes are created automatically and contain as many tracks as you have that fit the mix. When you select the Genius Mixes item in the iTunes sidebar, the main area of the iTunes window displays your mixes. Each mix is displayed as a composite album cover; mouse over a cover to view, at the bottom of the window, the name of the mix and a sampling of artists it contains ("Based on Coldplay, Travis, Keane, & others," for example). With my library of 14,000 or so music tracks, iTunes created the maximum 12 Genius mixes--with smaller libraries, you end up with fewer--with names such as Rock Mix, Electronic Mix, Alternative Mix, and Alternative Mix 2. Click on a mix to being playback.