Video wallpaper (background)

if you like using battery unnecessarily .

This along with things like customize icons will never be in the app store because of apple's rule not to allow tinkering with the code.

I doubt it.

There is of course a version for jailbroken units. I don't think the battery hit would be all that much, since it is only for the home screens. Unless you spend a LOT of time perusing your app icons...

Officially, it's not viable.

Apple's SDK terms and conditions state any customization of iPhone OS's UI, other than the abilities found in the January Software Update, are prohibited.

Applications are sand-boxed, and cannot tamper with system code.

R-Fly