I wrote code for this ten or so years ago. I don't say that to brag, but to express my annoyance at every credit card form I encounter on the internet. Why do you ask me for my number and what type of card I've got?

Well, people are conditioned to expect it now, so taking it out could potentially have adverse effects. Might make an interesting A/B test.

github actually does a pretty good job:

http://skitch.com/dlsspy/rkwab/plans-and-billing-github

How about just putting the form for the number first, and the let the drop-down menu for the type of card automatically select the right type---while still allowing user interaction.

The worst ones do half of each -- they tell you that you entered a Visa and didn't press the Visa button and ask you to go back and press the Visa button. Thanks.

Came here to say the same thing - wrote a validator in Pascal at least 15 years ago - why this isn't more automated these days is ridiculous.