So, there's some strange behavior. It seems the refresh rate of the device file increases as the button press-rate increases, but to what extent i don't know because i can only press the button so fast.

So, here's a very basic app to poll presses and report the frequency and approximate speed (based on 2m/revolutiion). Do you have a "real" bike computer to test its accuracy? If not then if you could check to see that it seems to scale up to higher than 5 Hz accurately, it may be worth putting more time into (i.e. GUI etc). I ended up stripping out everything besides a basic polling loop, so it's very simple right now.

Suggested means of basic testing (in absence of "real" bike computer): flip bike and spin wheel. Note speed reported. Increase speed of spin slightly and check that reported speed increases slightly. Repeat...

Oops, to run the app, type /opt/maemo/usr/bin/maebike.sh. I forgot to take out the trigger file so you have to run that script twice after you kill the app (ctrl-c) to run it again.