Human Computation and Cognitive Surplus: Social Media Theory Series: Part 2

Two people I really admire in the Internet space are Clay Shirky and Luis von Ahn. I have read few books from Clay Shirky but never met him. However, I got a chance to meet Luis when I was in C.E.R.N., Geneva. He is a very energetic and has a hard to miss personality. He came to give his talk on Human Computation.
Shirky talks about cognitive surplus in one of his book. He talks about the way television was/is occupying the free time of people and giving them entertainment where they had very little to do. (being a couch potato). This free time which people with an urban lifestyle spend on different entertainment sources, he calls it as the cognitive surplus!
He further says that how tools like wikipedia have tapped a fraction of that cognitive surplus and able to create something greater for the public use. The idea of cognitive surplus is fascinating and he talks about the origin of the same in his book apart from other ramifications.
Also, Luis at the same talks about how his bachelor’s thesis on creating CAPTCHA made so many online users  filling text after manually scanning the images. How he realized that he has so much human computation available at his hand when people are scanning these images. How people in the spamming industry were using porn sites to decode the CAPTCHAs and how he started using it for scanning books (reCAPTCHA). He also created a game known as ESP ( http://www.gwap.com/gwap/gamesPreview/espgame/ ) which is another fascinating story of tapping into human computation to better tag images.
When I travel in Delhi Metro everyday. I feel there is so many free hours available through the riders of DMRC but no body is tapping them! In 2008 I got to know that in Paris 13% people find their soulmate because of Paris metro (RATP). I think there is a game (an interesting problem which can be solved using human computation) waiting there to tap cognitive surplus of DMRC riders (average daily ridership of 2.3 million) .
What is your game idea to tap into this cognitive surplus? what is the problem that you can solve using human computation?
Cheers
-sachin