That's what I thought of too -- Microsoft's DreamScene.I don't mean to curb our enthusiasm (the idea sounds terrific) but isn't this a feature that "sort of" exists in Vista?
Doesn't sound exactly the same, but IMHO, it's close enough that some people are going to say that Apple copied the idea from Microsoft.
http://www.microsoft.com/windows/products/windowsvista/editions/ultimate/default.mspx
More Windows Ultimate Extras coming soon
* Windows DreamScene, an Extra that enables you to use looped, full-motion video as your desktop wallpaper instead of a static image