I never wash my chickens before I cook them. Sometimes I think it's out of laziness but mostly I just don't see the need: Any bacteria that might be present will be killed during the cooking process. Besides, you really shouldn't be buying chicken that is so questionable you feel the need to wash it. Plus, isn't the risk of cross-contamination from the chicken-y sink so much greater than the possibility that a chicken cooked to an internal temperature of 165° F will make you sick? Why is it, then, that so many cookbook recipes for chicken dishes start out by saying, "Rinse chicken well and pat dry." Even the USDA says there is no reason to wash raw chicken.
So why do so many people do it?