A lot of people commute on road bikes into DC -- I know because I see a dozen of them each morning and probably dozens in the evening.

It's not my thing - because I hate skinny, hard tires on bad roads -- but it doesn't seem to bother most people I see. I'd say 90% of the commuters I see are on skinny tires, no fenders, and have a back pack on.....all 3 of which I hate.