Though I think I'm going to setup my xserver so that I can control all three keyboard LEDs, and do something mathematical and geeky with them.
This was inspired by Cryptonomicon, by Neal Stephenson, in which the main character surrpetitiously communicates with a computer while being spied on (he can't put the data on screen, he can't type in commands without it being monitored by someone). So, he writes a program that allows him to give commands using morse code and the space bar, and get output using morse code from the scroll lock button.