How can I use shortcuts like Windows+D to show the desktop or Windows+E to explore, Windows+S to search on Ubuntu?
I've always used xbindkeys. Very simple syntax and you can port your settings to any machine capable of running UNIX-compliant code (Linux, BSD, OSX, etc). Just find the terminal command for whatever you want to do (many/most GUI Linux applications will also take terminal input, check the man pages), then bind it to whatever key combination you want.
And don't forget to add xbindkeys to your startup options.
You'll probably have to set the shortcuts yourself...
Go to System->Preferences->Keyboard shortcuts.
On this screen you can specify a lot of keyboard shortcuts and their key bindings.
(Note: In Ubuntu or other Linux distros the "Windows" key is called the "Super" key)
The Ubuntu documentationhas all the details. I am not an Ubuntu user myself, so I can't tell you how easy or difficult it is. But it looks like a five minute job. Check out the link.
Taken from the above link:
Win+E -> Home Folder
Win+L -> Logout
Win+F -> Search
Win+M -> Hide all windows and focus desktop
Win+D -> Hide all windows and focus desktop
Nice find Saikat!