I think you forget the core value: listen to your music everywhere.
That isn't compelling?
That isn't compelling?
Then I got an iPod.
And I can't see why Google didn't go farther. Whatever Apple's rebranded MobileMe turns out to be, it's almost certainly going to be more ambitious than Google and Amazon's services. Google has to know that. I just don't see why they didn't really act on it.
Now I just need my phone to auto-realize it's in the car and start playing music over Bluetooth or something to the car stereo. Too bad I have an iPhone - if I had an Android I'd be tempted to implement this myself.
Has Android and iOS clients, and is also accessible via the web. It's not as clean and polished as I'd like, but it works reliably enough for my tastes and is fully open sourced.