Very nice. But your preview visualization uses what I assume to be close to final art, including all the flaps and all. With web inspector (and some curl) I was able to extract all the layers, combine them together, and get a printable file:
http://cl.ly/JprNI'm sure most of HN visitors would be able to do the same. Not sure if you should patch it, though: your target audience will surely won't do things like that, and visualization is already a complex beast.
Anyway, thanks for the free foldable design (: