In the continuing blurring of the lines between web and desktop, Apple has moved the iTunes Store in iTunes 9 to use WebKit as its rendering engine. I was actually surprised to learn this was not always the case, especially with Apple adding Safari for Windows a while back.
The rest of iTunes remains a custom desktop user interface, but it would not surprise me to see iTunes 10 be completely rendered using open web techniques. We already see competing products like Songbird using open web technologies for rendering media players, and it could eventually lead to a version of iTunes that lives inside Mobile Me, with songs stored in the Apple cloud.
Given Apple’s recent push on efforts like Time Machine and Mobile Me, it seems like Apple is working hard towards the important goal of making it very easy for users to not lose their data and work, and moving the iTunes franchise to the web would seem to be the next logical step!