What is it about a doorknob?

We were In Marion for the 4th of July specials and stopped at a store that had architectural salvage.  This store had a wonderful way of displaying door knobs in frames, boards and cupcake holders.  Come to find out the owner is enamored with doorknobs!  I start to share with him that I love doorknobs and the most unique one had a geisha girl surrounded by an umbrella and he knew the exact  set I was talking about.  Apparently I had (sold) the ever sought after Geisha Girl.   He then hands me an application for Antique Doorknob Collectors of America brochure.  Who knew!  I guess there is a collectors club of just about anything.