Interesting thread.

Some years ago, I was at my local field with a friend. At the time, he was flying a .40 sized sport plane with a 46 IC engine. He had installed a new, differenty type of propellor. On his first flight he noted that the airplane seemed slightly slower, and there was a strange "whistle" that wasn't there before. He kept that prop on the airplane for the next couple of months, figuring that the whistle was normal, as we didn't observe any damage to the prop, and it was well balanced.
It wasn't for quite some time that he realized that he had mounted it backwards, I.E. with the trailing edge of the prop pointing foward. It worked, but after installing it correctly the plane picked up speed and was less sluggish. So they will work backwards, just not quite as well.