A mirror should never face the bed (it's like inviting strangers into your relationship).

It has to do with the spirit leaving the body at night.  There are different spirits moving around at night and the reflections will shock and multiply them.  One of them may end up in bed with your wife!!

Isn't that kind of gullibility that makes people easy victims of market manias and bubbles?

Something like believing in Jesus Christ and that praying in church will save you from cancer? 

BTW, I don't truly believe in any of this.   But there's nothing wrong with creating a harmonious pleasing living environment.   Clutter is also very bad and is the worse source of bad chi/energy.   It's best to have an organized, clean and free flowing house.   I have seen some Asians who believe in Feng Shui, yet keep very cluttered houses.  With the clutter, they obviated all the good architectural Feng Shui.