I'm the only year-round commuter at my office, but there are 3-4 others who ride when it's nice (5 miles or shorter commutes). My commute's 14 miles each way, so they all think I'm wacko. I pass alot of commuters, though. I ride against the normal flow of commuters into DC, so I'm not passing them because I'm fast.

I personally know 7 bike commuters.