A fascinating TED Talk by Rosalind W. Picard of MIT, who really* cares about what you feel.
https://www.youtube.com/watch?v=ujxriwApPP4
Cool stuff since some believe, overall, emotions truly determine your reality (http://www.bewellbuzz.com/author/jonni-laforce/) (since your reactions come forth into the real world as a result of what is buried inside and hidden from others etc.) <-- via this TED talk by Jonni LaForce (https://www.youtube.com/watch?v=qDa0rFvtjEE)
*Unlike the selfish hopes of product marketers who probably want this kind of tech in every home and on every person ;) -- see http://www.affectiva.com/news/ (via http://www.forbes.com/2011/02/28/detect-smile-webcam-affectiva-mit-media-lab.html )