Wow.. super cool.. you can store your music on your iDisk and then just access it through your phone and it even works in the background now. If they start adding more features like this I might have to get MobileMe back.
http://www.engadget.com/2010/08/04/apple-slyly-enables-background-idisk-music-streaming-in-ios-4/
http://www.engadget.com/2010/08/04/apple-slyly-enables-background-idisk-music-streaming-in-ios-4/