I just received my Jan/Feb 2008 issue of Bicycling magazine, which includes a section on commuting. It references the website for SmartTrips, a Colorado based commuter advocacy group. The site has a calculator you can use to see how much money you save, calories you burn, and pollution you reduce by leaving your car at home! Visit http://www.smarttrips.org/transportation/savingsCalculator.aspx. A cool tool, though the fuel savings is based on old gas prices (.73/gallon from June 2006).