My first thought was a 4square like site with "geeky categories" for check-ins. You get more points the geekier your check-in is. A large national museum gets you some points, a local museum gets you more. Same with big city vs small rural book stores or comic shops.

Tech stores get you a few points, locally ran places, the type with computers lying open everywhere get you more.

Also worth points, corporate headquarters, conventions, and libraries.

Or, go deeper. Do this with a browser plug-in, and count websites people visit, and length of time spent there. Yes, game analytics. Sell the data anonymously. Spending time reading Wikipedia is one thing, spending it logged into GitHub is another. Rack up geek points for the above mentioned categories too.