Comment 3 for bug 389754

ctrl-alt+d should hide all windows and show the desktop. What games/applications in fullscreen is this not working for you?

Lightbreeze wrote> You can change to use windows key+d under 'System > Preferences > Keyboard Shortcuts' and scroll until you find 'Hide all windows and show the desktop background'.

Bug #12153 proves me wrong. You cannot use win+<key> for any keyboard shortcut - for the moment.