Years and years ago, I bound a function key in my window manager to start xlock and then carefully trained myself to hit F10 (the aforementioned function key) the moment I got up from my chair to leave my cubicle-office. It didn't matter how trivial the errand or how short it would be; I'd hit F10 and locked the screen. By now I have this habit so ingrained that it's become one of my little twitches.

We have an access-controlled office area and everyone in here is some sort of system administrator, so it's probably pretty harmless to not lock your display when you walk away from the computer. Probably.

The reason I bound starting xlock to a function key was to make it as fast and easy to do as possible; the faster it is to lock my screen, the more likely it is that I'll do it all the time. No exceptions, no 'I'll just be away for 30 seconds and it'd be too much of a pain to find the menu entry'. I figured this was well worth stealing a function key away from programs that might want to use it.

(This reminds me that I need to turn off the automatic display locking timeout on Fedora Core 5, because it interacts badly with a KVM; I'm a bit tired of finding the display on my test machine locked just because I switched to another machine on the KVM for a while.)