It's been one heck of a ride...we're web guys and don't exactly have a lot of experience in building factories or making, um, real physical objects.
The frontend is powered by Interface (http://www.getinterface.com), with the backend order fulfillment / manufacturing infrastructure built in Rails running on top of Ruby 1.9 and Unicorn, all sitting behind Nginx. All asset processing on the backend is done using GraphicsMagick using a modded mini_magick, which is way faster and more efficient than ImageMagick.
We'd love to hear your feedback, thoughts, and criticisms!