As with all technology, there's the good and there's the scary. Facial recognition software can now detect your mood. And one good application would be for teachers to detect when a student is struggling with an onscreen lesson. See Facial Analysis Software Spots Struggling Students -- A computer can learn to recognize, and respond intelligently to, users’ emotional state:
A recent study from North Carolina State University shows how this might work. Researchers there used video cameras to monitor the faces of college students participating in computer tutoring sessions. Using software that had been trained to match facial expressions with different levels of engagement or frustration, the researchers were able to recognize when students were experiencing difficulty and when they were finding the work too easy.
If the technology is available it's probably a safe bet that the casinos are already using it to study the faces of the whales at the tables as they try to maintain their poker faces. Then there's the NSA. Not only will they know what you're looking at on the 'net, but they'll know how you feel about it.
Oh, do I sound paranoid? Well, let's just say Hal, the space age computer of "2001: A Space Odyssey," made an impression on an impressionable mind.