The Grid view is flashy, but the real game changer in iTunes 8 is Genius. Genius comes in two guises, Genius Playlist and Genius Sidebar, and is similar to music recommendation offerings by Last.fm and Pandora. If you choose to use Genius, which is optional, a few things happen. First, it analyzes your iTunes library and transmits that data, anonymously, to the Apple's servers. That data is compared to data from countless other iTunes 8 users, and fed into Apple's Genius algorithms. The algorithm then reports the results back to iTunes, which uses it to create Genius playlists of 25, 50, or 100 songs, based on whatever track you select. You can listen to that playlist, save it for later, or hit Refresh and have Genius create another playlist that is more to your liking. Much like Party Shuffle, you can delete songs that you don't want to be included in the playlist, and re-order the songs.
After creating countless Genius Playlists, I am a convert. This is a great way to rediscover music that has been hidden away in the depths of your iTunes library, and it groups songs that I would never think of grouping myself ("Veronica" by Elvis Costello goes well with "Debaser" by The Pixies--who would have thought?). Genius did an admirable job of creating playlist after playlist with almost everything I threw at it (including a song by Raina Rose, a folk musician who also happens to be my girlfriend's sister).
When Genius can't create a playlist it pops up a warning, and suggests that you update the Genius data on your Mac. Classical music, in particular, seems to stump Genius. And since this initial version of Genius appears to derive a lot of its data off iTunes Store purchases, songs by artists not in Apple's online store--like, say, the Beatles--can also flummox it. Click on a tune by the Fab Four, and Genius will be unable to generate a playlist. Presumably, as the feature gets more data from more users, issues like these should, theoretically, become moot.
The Abbott to Genius Playlist's Costello is the Genius Sidebar, which marries the iTunes Store's Just for You recommendations to the mini-store interface that was introduced in iTunes 6. The Genius Sidebar takes the currently playing song and, using that fabled Genius algorithm, returns recommendations from the iTunes Store. The recommendations include songs and albums you might be interested in, as well as songs that iTunes believes are missing from your library (for example, perhaps you only purchased one or two songs off of an album). I've found myself losing a number of hours checking out songs that the Genius Sidebar suggested. You can preview songs right in the sidebar, while you have to go into the iTunes Store to check out albums. Both can be purchased with one click in the sidebar, so you should either disable 1-Click purchases or practice restraint.
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