Sensing component company Omron has created what it calls "smile measurement software," which rates the amount of happiness that human subject of a photo are exhibiting. On the face of it (ouch!), the applications aren't too obvious: then you consider that this could easily be used by robots to detect their owner's -- and future slave's -- state of mind, even if it is on a rather polarized scale.
http://www.engadget.com/2007/09/09/omron-announces-smile-measurement-software/
http://www.engadget.com/2007/09/09/omron-announces-smile-measurement-software/