Having used Amazon Cloud Player quite a bit, as well as other similar web services (lala, grooveshark), I can say that Cloud Player is the worst web based music player I've used. Can anyone comment on Google Music, or iCloud?
That said, I've recently realized that I don't really like my music. That is, I'm much more interested in effective music discovery apps like Pandora, Grooveshark, and Turntable.fm.
Can't wait to see the Google+ spin on Google Music...