Actually, it tracks MMOs, but what a clever title, huh? The Daedalus Project is the demographic/analysis website created and maintained by Nick Yee, a graduate student of Stanford University in the field of Communications who now works at the Palo Alto Research Center (PARC). Nick's site is noteworthy both for the online surveys of MMO players that are open to anyone who wants to participate, and also for the conclusions he draws based on those survey results.
This statistical data has been used by Washington Post, CBS, TechWeek, CNET, the Associated Press, Nature.com, the New York Times, and the Wall Street Journal, among other publications. Nick always has a survey or two running, so if you're interested in contributing your experiences and thoughts to the collective (and growing) body of knowledge concerning MMOs, you can do so at the 'Current Surveys' section of his site.
For those of us interested in metadata, The Daedalus Project is a genuine boon, and we hope he continues his necessary and groundbreaking work well into the future.