While compiling KDE for a new Gentoo Linux system, reading e2 in lynx, chatting in BitchX, and working on a perl program the other day, I found that the windows keys on my keyboard had acquired a very useful function: they switched between virtual terminals. The "application key"* could also be used to go back to the previous terminal.
These keys allowed me to switch between tasks before I even knew that I wanted to, since they were easily accessible whether my hands were in the regular typing position or just on the arrow keys**. I have never seen a better use for them.
* The key between the right windows key and the right ctrl; this is the only name I've ever heard for it. Does anyone know a better name?
** The arrow keys in lynx are used to follow links, go to the previous page(s), and move up and down on the page. Other keys are rarely needed.