Would you let device cameras observe your reaction to how you are using them?

While listening to the "This Week In Tech" podcast (https://en.wikipedia.org/wiki/This_Week_in_Tech) a comment was made that I had not thought of before. It had to do with phones, tablets and devices in general using their cameras to determine your mood and this being extended to Google Glass, Microsoft Kinect and so on. I've used the Philips Vital Signs App (http://www.vitalsignscamera.com/) in the past for determining my heart and respiration rates but had not considered this sort of capability being utilized by game and other applications to potentially enhance your experience or report back to a data collector. Advertising companies use website log data to evaluate customer behavior and pages that either hold, redirect or repel people. Imagine if the devices around you used this same thing to determine if you are interested, confused or bored. If an app thinks that you are confused by what you are doing it might add a level of interactive support or conceivably automatically engage their customer support. This of course has all sorts of implications for privacy and so on but is inevitable and hopefully beneficial.