Waterloo Labs, a collective of insane National Instruments employees, developed an electrode system to measure eye movement, and then used that as a control method for Super Mario Bros. Look past the break to see it in action -- you'll also have to click, unless you're wearing one of these setups.
The result of Waterloo's project is the ability to move Mario just by moving your eyes in the direction you want him to go. It's less "a practical experiment" than it is "fodder for an awesome video" -- although it's not hard to imagine technology like this being useful to players with limited mobility; or as an extra layer of augmented-reality control. And, if nothing else, it's just something cool to do with all those electrodes you might have lying around.
If you happen to be attending National Instruments' NIWeek 2010 conference in Austin, Texas this week, you can see this technology for yourself! Or you can build your own using the group's design documentation.