I almost never use the function keys.
If you didn't know already, in Linux console mode, Alt-Fx key switches between virtual consoles. If you have X running, then one of them usually goes (back) to X.
Some window managers for Linux/X therefore have Alt-Fx mapped to switching between workspaces, per default, and I used to have it that way for years. These days, I have them mapped on Alt-numeric row instead, so that I don't have to stretch too far.
I also used to map Previous track, Play/Pause and Next track to Scroll Lock, Pause/Break, and Print Screen, respectively for my mp3 player.