Reaction time experiments are widely used in psychology. For serious use, it's important to have a very accurate measuring device. Standard keyboards are not made with timing accuracy in mind, so psychologists use special 'response boxes', such as this one: http://www.pstnet.com/hardware.cfm?ID=102
It's very accurate, but it works only with special software, connects via serial port, needs drivers, and - it's pricey.
I'm guessing the new Leonardo could be made into a nice, accurate reaction time measuring device. The most user-friendly way would be to make leonardo emulate a keyboard, so it could be simply plugged in.
Also, some low-bounce buttons should be used.
So, does someone know lag-times for the leonardo - how much time does it take from pressing a button on the arduino to computer receiving the button-press signal? If it is long - could it be made shorter?
How about low-bounce button designs?