I've seen those and they annoy the heck out of me. Especially when they are charging a fortune to stay there. The one that really got me though was the hotel (don't remember which one now) that asked me to leave all dirty towels on the floor and they'd only change those.
I guess the cleaning staff (who have never appeared to be THAT incredibly stupid - but maybe I'm missing something...) can't tell whether or not a towel has been used! Sheesh.
I really contemplated throwing every towel on the racks down on the floor, just to make them change all of them.