2 words: Xgl and Compiz.
Xgl is a hardware accellerated X server created by Novell. Compiz is the first compositing Windows manager. These power tools combined enable the 3D Desktop. (Unfortunately for those of us using windows, this software is only available on Linux.)
Some effects you can create with the Xgl/Compiz combo are:
The scale function allows you to see all the screens you have open, except for when it's minimised, in which you would use the traditional Alt-Tab function.
This function enables you to treat the desktop as a cube where each side is a virtual desktop. This makes it easier to remember which application is located on which virtual desktop and it helps to organise the running applications better.
Check out this website for installation details:
Check out this cool feature below: