Billboards Look Back

http://www.wired.com/gadgets/miscellaneous/news/2007/06/eyetracking

"The eyebox2 from xuuk is a palm-size video camera surrounded by infrared light-emitting diodes. It can record eye contact with 15-degree accuracy at a distance of up to 33 feet. A simple glance from a passerby scores an impression, providing a tally that enables new Google-like measurement metrics that real-world advertisers could only dream about until recently."