There's no denying the popularity of iTunes - it could be said that iTunes single-handedly took down the record store business model. But think about it. iTunes isn't even a website that you can surf from anywhere. You have to have iTunes loaded onto a computer (or iPhone) before you can buy tunes.
This will be great for everyone. It will be more convenient for users, who will no longer be tied to a specific computer. It could bring about a huge boost to Apple, who'll be able to link to other websites for one-click shopping for songs.
Similar to how you can buy a song used on YouTube from Amazon's music store, imagine listening to Pandora and with one click, purchase a new tune from iTunes. Until this launches, you've still had to launch iTunes on your computer first. This will be uber-easy.
The cloud-based iTunes.com could launch in just a few months. Will you move your library into the clouds?