The interesting thing about ITMS is that it is integrated so tightly with iTunes, and that iTunes itself is a pretty slick program.
Perhaps Apple is still working out the bugs, but the initial rollout of ITMS is missing a huge opportunity: recommendations and aggregation.
Amazon already does recommendations based on what you’ve bought and what you say you like. And audioscrobbler (thanks to iScrobbler) keeps track of exactly what I’ve been listening to, and makes recommendations based on that using some kind of collaborative-filtering hoohah.
iTunes also keeps track internally of what I’ve been playing. ITMS could roughly duplicate what audioscrobbler does and let me preview/buy the recommendations directly. That would be slick. iTunes also allows one to assign star-ratings to songs, but that’s a little tedious, and the audioscrobbler philosophy–that what you listen to most is what you really like the most–is probably more honest.
Likewise, Apple could aggregate this data into a form that it could sell to the record industry. This raises obvious privacy questions, but frankly, as long as it would be anonymous, I would be perfectly happy for the record industry to know that I have never, not once, listened to Britney Spears, N’Sync, Alan Jackson, or whatever–but that I do listen to Beck, the Asylum Street Spankers, Caetano Veloso, etc.
It’s also funny to see how they categorize music, since (once you get past the front page) the store uses the same genre/artist/album column-browser as iTunes uses for your own music library. Jimmy Cliff, Jon Secada, Martin Denny, and Abba are all listed under “World music.” Putting music in pigeonholes is often unhelpful, and that particular slot is especially so.