I use the Microsoft Natural series of keyboards on all my computers, and frequently switch between Windows and OS X. I have it mapped so the keys are in the same places as the Mac keyboard (meaning Ctrl == control, Win == option, Alt == command) since that's the OS I use most often.[/size] This workflow lets me use the Win+key combo to perform the most common system functions I use regularly:
Win + L: Lock screen
Win + U: Shut Down
Win + R: Restart
Shift + Alt + F4: Quit all
Ctrl + Shift + Esc: Application Monitor
The same keys work on the Mac keyboard, just with different names on the keys:
⌥ + L: Lock screen
⌥ + U: Shut Down
⌥ + R: Restart
⇧ + ⌘ + F4: Quit all
˄ + ⇧ + ⎋ (␛): Application Monitor
You can download it at https://github.com/morganestes/alfred-windows-hotkey.