Google patent allows Glass to track ad views3
Google expects "pay per gaze" to be used to track how many times a billboard or an ad in a magazine or newspaper was looked at. Google does anticipate some privacy problems though, and the patent notes that Google Glass users will be able to remove their personal data before their "gazes" start adding up to advertising dollars for Google. Additionally, if the Mountain View based tech titan does decide to forge ahead with this, there might be a plan to allow Glass users to opt out.
source: USPTO via MarketingLand, TheRegister