iCloud

I'd imagine you'd still have actually copies on your computer to sync with your devices. That's how I'd rather have it anyway. Cloud music is good but I'm not always in areas of cellular service.

 

It seems that it will be kinda remote storage, synced with all your devices, with streaming capabilities. I.e. once you listened to track, it should be saved on your device. Without caching it would be almost unusable.

 

Two things have to happen before cloud computing really takes off, although Apple is one of the best companies that could do it software-side. Those items being (a) connection speed; and (b) connection cost. If you could pay for a T1 or comparable connection for most of the already connected populace (if such existed for wireless connecting) for less than $70 or 80 a month, it might work.