Credit card numbers on the cards themselves seem to follow a pattern--four clusters of digits separated by spaces. This seems to comport with "human factors engineering" that I think shows people have difficulty remembering more than four digits at a time, like, when one is reading the number out loud to a customer support soul.
Yet on web forms of all kinds, users are instructed to enter their credit card number without spaces, without hyphens-=-just 16 digits in a row. I.e., when "retailers" are collecting the most important piece of information from the buyer--they're making it nearly impossible for the user to verify her entry of a 16-digit number.
I have heard that some people make CGI scripts 'n' such to check up/validate input in information/data fields. Surely they can make a script that will accept spaces or hyphens in credit card numbers, then strip them out for the IT folks in the computer room. This makes it easier for the user to enter and double-check his entry before hitting "submit" or "cower" or "send"--and it gets the 16-digit string, no spaces, to the legacy computer system which no one knows how to program any more?
And one gratuitous question: Aren't user interfaces supposed to be designed to make things easier on the user who's trying to use the interface? A bad UI or GUI is like having a hammer with no handle. Sure, you can pound nails with the unadorned chunk of steel called the hammer head, but it goes a lot faster with the handle attached--and one that's not so long that you can't pound a nail with it, either--the goal here being driving nails with arms too short to box with God--but long enough to hold a nail in one hand, whilst starting (setting?) the nail with that first tap.