Here is a way to show and hide the desktop with a simple bin bash script and a .desktop file. First you need to get the program wmctrl because it will be the program handling the desktop effect ( minimize all & maximize all).
Code:
apt-get install wmctrl
then after that installs run nano (or another editor) correctly and type the following script:
Code:
if wmctrl -m | grep "mode: ON"; then
exec wmctrl -k off
else
exec wmctrl -k on
fi
Save the file to: Desktop.sh (or whatever) and then put the script in bin bash dir (for instance I'll put mine in the home dir for now). Then create a new .desktop file and type in the following:
Code:
[Desktop Entry]
Name=Desktop
Path=/home/oddacon/
Exec=sh "desktop"
StartupNotify=false
Terminal=false
Type=Application
Comment=Show and Hide the Desktop
GenericName=Desktop
Icon=user-desktop.png
Tada! 
don't forget to include:
at the top of the .sh script!