That was cool. I just mapped my foot pedal (Kinesis, in case you were going to ask) to send nothing on press, and space on release. So I caught up on lots of LJ with very little hand movement. I can rest my foot on the pedal most of the time, which feels better than hovering, and just release it to page down. Sort of like a brake pedal. It's not helpful for typing prose (maybe code), but great for leaning back and browsing /. or LJ.
I'd fiddled with it once before (came set up as shift, which is really hard to get used to), to send space on press, but it would fall into key-repeat way too easily. The release event never gets repeated, so it's more controllable this way.