How MailChimp Picked 600+ Email Templates from a Pool of 700,000

If the answer does not involve A/B testing I will be upset.

[Turns out it is a bit more clever and probably less effective -- they used a rules system to eliminate "obviously" poor designs and then ranked the rest using Amazon Turk. Points for innovation, but I'm skeptical that people are good judges of what they find to be beautiful, as weird as that sounds.]