In Gnome the show desktop is by default mapped to ‘Ctrl + Alt + d’, if you would like to change it to something else the easiest way out is using the ‘System –> Preferences –> Keyboard shortcuts’. Though this is the easiest way those of you who are like me, would like to use the ‘Windows Key + d’.
This is not possible using the ‘Keyboard Shortcuts’ window as it shows ‘Windows Key’ as ‘Super L’ and does not allow to enter any additional key, so to acheive the ‘Windows Key + d’ for ‘Show Desktop’ you would have to run the following command in the terminal to get that done:
gconftool-2 -t str --set /apps/metacity/global_keybindings/show_desktop "<Mod4>d"
Thats it, hope you found this useful, let me know by writing down a comment below.