This is right up my alley. I love stories about our collective superstitions - things we take way too seriously, but for which the rationale doesn't add up. Bike helmets and airport screenings come to mind. And now, apparently, hand washing:

The end result of all this obsessive handwashing activity is that faecal bacteria are present on 25% of hands in Britain, with 11% of these hands containing more such bacteria than the surface of a toilet bowl.

I remember reading a long time ago that it would make more sense to wash your hands before you pee than after, since your weiner is probably a lot more clean than your hands. But that doesn't seem to be the common practice.