If these can be rented by the hour, it could be a good way to get Windows machines for testing websites with various versions of Internet Explorer and testing emails with various versions of Outlook.

I know that EC2 and Rackspace has Windows machines, but only with Windows Server. When I have tried that, there is always something funny, such as IE security settings that are different from those of desktop Windows installs.

For now, I have settled on having local Windows installs (free licenses through BizSpark) in VirtualBox.