What desktop for desktop previews (like Ubuntu/Mac)

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http://forums.fedoraforum.org – On a mac you can press a hot key and see previews of your 4 desktops. On Ubuntu 12.04 Unity you get this feature as well. Windows 7 is missing it (cry). I downloaded and installed the Fedora 17 KDE iso and it has virtual desktops (of course) but I saw no preview option. I'm downloading hte Gnome version now to try. Do you know if any of them have this feature? (HowTos)