Personally I find the Windows key relatively handy, as I try and use the mouse as little as possible (since I have my hands on the keyboard most of the time anyway). Here are some more uses for it:
WinAmp has several plugins that allow you to control it using the Windows Key, but by far the most useful I've found is BlueCave WinAmp Slider. Its main purpose is to allow WinAmp to perform pretty transitions when you minimise or restore it, but it also includes a very configurable hotkey utility. I've found that the best way to use hotkeys is simply to map WinAmp's existing hotkeys as Windows key shortcuts, like so:
Win+ctrl+Z - prev track
Win+ctrl+X - play
Win+ctrl+C - pause
Win+ctrl+V - stop
Win+ctrl+B - next track
Win+ctrl+S - toggle Shuffle mode
Win+ctrl+J - pop up 'jump to track' search box
Win+ctrl+Q - volume up
Win+ctrl+A - volume down
All of these shortcuts can be mapped without using the Ctrl key, with the exception of Win+B, which appears to have some function on Windows XP. I've included the Ctrl key in all my mappings for consistency.
The plugin can be downloaded
from winamp.com, in the plugins/General purpose section.
In Windows 98 and above, WIN+D takes you to the Desktop. The operation is similar to WIN+M, but also gets rid of dialog boxes and unminimizable windows (these usually spring back up again once you unminimise any windows though)
Something that needs to be developed is something which allows the WIN key to be used for custom macros, shortcuts and so on. Who needs a tacky 'programmable' or 'net-enabled' keyboard when the option to allow programmability is already there?
And finally - in Windows Help, the windows key is not required at all. Simply pressing . (period) or , (comma) takes you to the next or previous topic.
Now...what about some uses for the 'right menu replacement key' - the one to the right of the right-hand-side Windows key? The only thing I've found that useful for is to escape right-click blocking on webpages (you know, when you right-click and a dialog box pops up instead of the menu)... just click on the page or use tab to select the link you want to right-click on, then press the key. Although right-clicks are blocked, the key is almost never blocked.