If you've ever used CloudApp, you'll know it is an amazing Mac OS X app for sharing files. There was sadly no equivalent for Windows, and I've since made my own client for it for Windows around the CloudApp API.
Very cool. I didn't get to use it because I use a service called dropbox which does exactly the same thing. The new windows 7 commercials make it seem as though it comes with some kind og cloud file sharing application.