My account also broke after 4 purchases. The first two were Courtney Milan's "Un-" books, and I could tell you what the other two were if I could see my Bookshelf! D'oh! I also had a heckuva time signing in to my account, wasn't able to get in until I clicked on my wishlist from my browser history. It kept telling me (even when I tried to request my password) that my email address wasn't right, but I was entering it via the browser formdata thingy not typing it by hand! I emailed the address they gave me and hope they get me fixed up soon. I have some more books I'd like to pick up.
I think they did intend for the code to be used multiple times, as I looked at the email I received back in December with it and they use the phrases "load your eReader and save" and "stock up!"
Thanks for posting your lists! I haven't read a hqn title in years, so I didn't know where to start looking.