You’re right – it’s always helpful to have someone else point out the other 20% that I’m always going to miss!

I don’t know why I never thought of munging the CC# data myself on the server side – it’s not too hard to get rid of whitespace, after all:). I also like the idea of figuring out their CC type for them – maybe I’ll save that for 2.0.

Your comment exemplifies the point of this post perfectly – even if it looks ok (ever after a revision!), it’s important not to take for granted what could still be improved.

gsub(/[^0-9]/,”",creditCardNumber)

There — you have now eliminated another class of errors which can frustrate the user. If you want to be particularly helpful, you can validate the number in semi-realtime (via AJAX or whatever). Also, is there any need to have folks tell you the card type? Why don’t you tell *THEM* the card type (which is predictable on the basis of the number):

Card Number: [input box]
Card Type: AJAXified read-only data (or, alternatively, AJAXified combo box)

Similarly, you can catch most of the typos before submission with :

http://en.wikipedia.org/wiki/Luhn_algorithm