Page Hunt is investigating the human search behavior. Launched in July 2009, the online game presents users ('page hunters') with a random Web page asking them to input search terms that will place this Website within Bing’s top five search results.
If the search query puts the page on the first place, then the user gets 100 points, on the second place - 90 points. For non-frequent successful queries, the player gets additional scores.
I find disadvantageous that there is no explicit competition as the user plays alone. I suppose, if the online game would be multiplayer, it would bring additional motivation for the user.
More information about the game can be found:
and on Technology review.
A publication to this topic:
H. Ma, R. Chandrasekar, C. Quirk, A. Gupta: “Page Hunt: Improving search engines using human computation games”. Proceedings of the 32nd international ACM SIGIR conference on Research and development in information retrieval, 2009.