This is more than a little bit freaky.
Google claims a system that can provide a reliable, low cost, and unobtrusive, eye tracking system could have a variety of useful everyday applications. In particular, it outlines a method for billing advertisers based on the number of times users look at an advert – either online or offline, via a billboard, magazine or newspaper. The pay-per-gaze technology is designed for use with a “head mounted gaze tracking device” such as Google Glass. By tracking eye movement, the device would be able to determine which, if any, of the identified items within the external scenes viewed by the user are advertisements and charge advertisers on a per-gaze basis.
But you’ll be able to opt-out. So it’s OK!