We started covering the Windows key back when the blog first started on February 23. (Recall that the Windows key by itself will show the Start menu; combined with different keystrokes, you can perform other useful tasks.)
One of the most useful shortcuts we covered is Windows key+D to show the Desktop. Related to that is a similar keystroke: Windows key+M will minimize all of the open applications that can be minimzied, showing only dialog boxes. Try it out!
(If you want to minimize only the current window, try this minimize shortcut.)