When I tried your system out, the customer is required to fill out their shipping address on my site's insecure page. Why not have them fill that out on your secure page? As a customer, I would not feel comfortable filling out my address etc. on an insecure page. Sure, it's not a credit card number, but still, I don't feel like sending out my name, mailing address and phone number across an insecure connection.
If there is some simple setting to change this that would be great. As it is, I can't use the product.
If I somehow messed up, and the address information is supposed to be filled out on your secure page and I just messed something up please let me know.
PS Besides that issue it seems like a fine product.