Google Trends charts approximate search volumes for specific keywords used in Google’s Search engine.
Using this I’ve put compiled a quick map comparing search trends for the Green Bay Packers vs the Pittsburgh Steelers in the month leading up to the 2011 Super Bowl. Purple States are those where the majority of searches were for Steelers, Green for Packers. The more intense the colour the higher the percentage of searches for that team.
Google warns the data comes with a size-able margin of error and may contain inaccuracies, but the map matches expectations pretty well – Northern States showing more interest in the Packers and Eastern States the Steelers.