I can only speak for myself, but I have seen neat ideas in-store, but thought, "hey, I can print this!";
Also I made adapters and used models of products allready available online.
I don't think this will result in everyone printing at home in a few years, but it allready shows that a 3d printer can produce usable parts and copying things can be done by a mediocre 3D modeler such as I am.
I think KDog is right, a business can compete (higher production numbers are cheaper with injection molding, fit better, look better, work out of the box), if they keep the price reasonable.
Perhaps 3D printing will change the current scenario, where a Adapter from the hardware store costs 20 dollars, but is made out of 2 cent wort of plastic!
;-)