I remember reading about the custom of tipping the lady in the kimono who welcomes you to your room and pours your first cup of tea at the ryokan - and my wife (who is Japanese) confirmed that this is indeed a custom at traditional ryokan.

Dutifully, I made advance preparations - I prepared an envelope with the appropriate money inside (I didn't want to appear vulgar in handing over the cash) and I attempted to give it to the lady after she poured our tea.... She firmly refused it several times until I gave up.

Other people who get tipped in Japan... Doctors, teachers and politicians.
Go figure.