I remember hearing that the Susan B Anthony dollar coin failed because there was no extra position in the coin drawer of cash registers to put it in. Can you image if every cash drawer now has to be redesigned to have different sized bills?

(I know, I know, it's not actually that big a deal. The drawers have removable inserts, but you get the point of it.)

(actually, on second though, automatic bill readers in vending machines, etc. would need a big retrofitting, that's probably much more a big deal).