The calibration didn't align the front and back 100%. I used Zoom: 3, Shift: 7 if that helps anybody else.
With any combination of zoom/shift settings, did you manage to get the calibration page to print out perfectly *centered* (horizontally centered, that is?) That's the factor that influences how accurately the front/back line up. For zoom 3 / shift 7, what browser / OS were you using?
Chrome / Windows 8.
So far I've had the best success with Safari, pretty good with Firefox & IE, possibly some problems with Chrome.
I'll see if I can try another browser soon.
Not yet. I'll think about that some, like a "master zoom" function. However the resulting wallets wouldn't size properly for the tamper-evident tape I sourced -- so you'd be obligated to use regular tape.
It was just a thought. It may not be doable. It's awesome as is

Since carrying it around in your wallet sort of defeats the purpose, my thought is probably bad, but maybe a function then to print a "public" bill that has only the public key and doesn't fold... that way you can carry it around without worrying that your funds will be stolen, even if your (physical in real life) wallet is. Both (the "secret" bill and "public" bill) would be able to print on one sheet of paper.
Anyway, just spitballing. I think it's really cool already. Cheers!