Today i am working on a complete redesign of a companies website where there is also a checkout process. While doing some research i found this article on Smashing Magazine about a study that had been performed by Baymard Institute among many webshops. Each of these test where monitors in different was and analysed with tester speaking there thoughts aloud.
The example above was given as a improvement in the design to give the user a more secure feeling of the form. As some visitors experienced parts of the shopping forms as not save. It is clear from the images that version B on the right is a improvement. Giving the credit card a different background and moving the logo of security next to the credit card form contains it as being more secure.
More great tips can be found here: http://uxdesign.smashingmagazine.com/2011/04/06/fundamental-guidelines-of-e-commerce-checkout-design/
Baymard Institute also have a research study specific for the checkout process on there website.