"Cloud" computing is OS independent. If you have to download anything to use it, then it is not cloud computing. When you use gmail or hotmail or when you go to flytertalk, you're using cloud technology. Doesn't matter if you you're using windows, mac, linux or whatever. There is nothing to download either.

Personally I don't see the point of web based file storage. Flash drives are so cheap these days. For $100 you can get 64GB of storage.