iTunes 8,, introduces a couple of things that point toward a future in which Apple branches out beyond its pay-as-you-go buying model for media. Are these a harbinger of new buying options that will appear in iTunes 9?
iTunes has had a "Party Shuffle" function for quite a while, with which it dynamically builds a playlist from your music on your hard drive. It was not (so far as I could tell) particularly intelligent about how it picked out what to play, however--Chemical Brothers could be immediately followed by Dave Brubek. It was essentially a glorified shuffle mode.
With iTunes 8, Apple has introduced the Genius List, which communicates with a cloud server about the contents of your music collection, then does fancy some background intelligence so that when you give iTunes a seed song, it is able to build out an automatically running playlist in which the songs have more of a similar character. And what's great is that you can do this on the iPod, independent of iTunes.
While a seemingly small thing, this actually fixes one of my peeves about iTunes--when you want something more tailored than a full shuffle but you don't want to switch to radio, how do you do it? iTunes has always had a fairly black-and-white approach--it's random, or it's exactly what you asked for. There was no in-between. Genius List fills this middle ground without the hassle of creating mood-specific playlists.
This is clearly treading into the same territory on which, though for the time being, Apple is mum on how the algorithms are doing their magic. Apple is currently restricting the Genius List to the contents of your current library, while Pandora is, of course, a streamed service that introduces you to new music and artists.
This brings us to...
The Genius Sidebar
The Genius Sidebar goes outside your library to introduce you to algorithmically generated recommendations from the iTunes Store. Again, Apple isn't saying much about how this is done, other than explaining that it bases recommendations on looking at your collection, as well as others' (so the more people that take part, the smarter it gets).
At the moment, these recommendations are available only with the usual 30-second preview, but it seems like just a short hop to get to a full streaming, subscription-based approach, living in parallel with the pay-per-song approach Apple has successfully used so far. Rumors have been around for ages that Apple will introduce a subscription service, and the Genius Sidebar seems like a simple way to step into that approach.
Most of the subscription services tried so far have done rather poorly to terribly for various reasons: price point, confusing DRM, confusing interface, lack of content, or just not having a critical mass of users to sustain them. If anyone can make it work, Apple can, and my guess is that iTunes is its step toward a full-blown subscription service in 6 to 12 months.