If you use google music, you can upload* up to 20,000 songs from your computer (iTunes/Windows Media Player/Music folder etc, as well as your amazon downloads) to their servers to be able to access it from anywhere (incl your android device)
All fine and dandy, if you have unlimited data, if you have a good enough network connection, if you can find free wifi that will let you log on/use it for more than an hour/actually stream data, (I’m looking at you, BT Fon).
[Edit]
you can upload* up to 20,000
What’s the point? I’ve got that many on my phone, and 160,000 on my iPod. 200,000, and I might be interested, and it would have to leave the bitrate at 320Kb, too, which is why I refuse to use iCloud.