I recently upgraded my ubuntu from 10.10 to 11.04. I use to issue the shortcut Windows+Tab key in my previous ubuntu version and the windows will be shown graphically through which I use to switch. But now that is gone!. Windows+Tab key does nothing. Do I have to do something to enable it back or I have to live with this :(
This happens because at Natty Mod4/Super is a shortcut to Unity panel. You can change that at Compiz.
1) Install Compiz Settings Manager
sudo apt-get install compizconfig-settings-manager
3) Go to Unity and change the shortcut as you like to free your shortcut:
At this example I've changed from Super to Super + L
Now your mod key is free to use as you like.