I would be really really interested how Gazehawk is doing the webcam eyetracking. Last year I decided to pivot my usabilitytest.com business to do exactly what they are doing now. I have been testing / researching / combining different eye-tracking and head-tracking algorithms/APIs etc. I must say for an engineer it was an ultimate challenge. However, after 3 months of working on it I realized this is too much for me and I called it quits. I managed to get eye-tracking working using 2 webcams (one front to monitor head-movement and one small near the eye to monitor eye movement). Unfortunately, because of the nature of eye reflection I had to work in complete darkness and use IR light to illuminate the eye - you can't call it non-intrusive method.

So I am very happy that guys at GazeHawk cracked this and launched the service that I really wanted to do and offer people low-cost eyetracking method.