I was at a hackathon over in Santa Clara recently where we were using consumer brain wave reading headsets: http://www.neurosky.com/

Unfortunately, it looked like there were something like 8 signals read, the two easiest being concentration and relaxation. Blinking was there too, although that had false positives and was even delivered as a probability more than a boolean. But hey, the tech is coming.

I like that. I think that's part of the appeal here. I don't mean the electrodes in your brain part, but that there is no friction between your volition and something happening on the screen.