To commemorate Bike Commute Week in California, San Francisco Mayor Willie Brown biked to City Hall yesterday, then took a limo ride back home for a shower. Eight members of San Francisco’s Board of Supervisors also biked to work (no word on where they showered). Nationwide, less than 2 percent of Americans commute by bike, says the California Bike Coalition. But biking enthusiasts hope to change that. They are asking commuters around the country today to pollute less, put on their bike shorts, and head out to their jobs in recognition of National Bike to Work Day.