This is pretty slick. The Tobii 1750 Eyetracker logs the activity of your eyes as you read/look at a computer screen. It could be used to improve useability as users interact with web sites and your software.
In the images below, the left one shows blue dots and lines where the eyes stopped and jumped to. Bigger dots imply more time in one spot. The image on the right is more of a thermal scan-like effect.