Equivalent for windows key + D in Ubuntu

http://ubuntuforums.org/showthread.php?t=87345
If you just want to know the show desktop short cut keys in Ubuntu is is: CTRL + ALT + D

If you want to map the "windows" key to the equivalent functions see this link:
https://help.ubuntu.com/community/MappingWindowsKey

Basically:
Create a file here /home/user/.xstartup
Paste the following in the file:
# Make the Windows key a useable mod key:
#xmodmap -e "remove mod4 = F13" # should not need this line
xmodmap -e "keycode 115 = Super_L"
xmodmap -e "add mod4 = Super_L"

Go to System -> Preferences -> Keyboard Shortcuts
Map keys (these are the ones I use fairly often)
Win+R Show the panel run application dialog
Win+E Home Folder
Win+D Hide all windows and focus desktop