Striking... you are right about the AirBnB [1]. Even Henry Ford said if he would have asked people what they wanted they would have said faster horses. Steve Jobs also was known to do as he pleased because users don't know what they want.

Not familiar with washboard. I will check it out.

Another interesting case is the founder of SnapInspect. He asked realtors if they would pay in advance for this solution. A few did... and now it seems to be doing very well.