Google is known for employing brilliant people and it seems to be precisely the case with Luis von Ahn, a professor at Carnegie Mellon. After initially explaining the concept of Captcha, Von Ahn moves on to the subject of Human Computation. The explanation of the thought process involved in specific case studies is amazing, real food for the brain. This Google Video from this specific Google seminar is well worth the time : I consider it a real privilege to have been able to see it...