Puzzlebox Jigsaw created by Steve Castellotti tracks your brain waves in both relaxation and concentration levels by its Neurosky's neurofeedback EEG headset.
Basically here's the skinny. If they can track how your felling during game play companies will be able to make things harder, easier, meaningful, fun, and even scary. Personally I can't wait to see how awesome a game can be when it is proven to scare your brain.