None of the global shortcuts work when I'm using any fullscreen game, including Alt+Tab.
I can't get out of the game until I use some kind of "exit" option, can't start/stop the music player...
This is especially annoying on my laptop, as fullscreen applications increase the brightness to the maximal value (which is another problem, but I think they have a common root), and I can't change it.
I use Kubuntu 11.10.
It seems to me in a lot of games this simply does not seem to work, it really depends on the game. The only hotkeys that work always are the global hot keys for switching to terminal, like Ctrl+Alt+F1 etc., I think it must have to do with how the other hotkeys are handled in Ubuntu, at least with certain hardware, in some games I can not even change my volume with the funct key. However in games like Ryzom all the hotkeys work, and even the hot corners work for showing all windows and showing desktop etc.
A solution that works for me:
There is a plasmoid called Show desktop. I assigned Meta+D shortcut to it. Pressing Win+D minimizes all windows, though it doesn't change the screen resolution (at least immediately).
After you pause the music or respond to an IM message - maximize the game window again.
Though it is really pity no one implemented this in Kwin by default.
