Jory Boling

I wash mine when it gets excessively dojo and I wash my wife's obi just to break it in. When I first started training, I was curious to see if a white obi would one day turn black (per the story about the origins of the black belt). Since then, I haven't placed any special significance on it, other than it holds my dogi closed.

Pertaining to the "what do they do in Japan" aspect, I think the mudansha always wash their belts. They are always very clean. I don't know about all the yudansha. Their belts are hidden under their hakama. They have that clean yet lived in look.