Another problem is the address format. US sites that ship internationally almost always require a state field - something that's not a part of the address here in Sweden. For sites with lots of international customers it might be better to let them format the address since there are a lot of different formats: http://en.wikipedia.org/wiki/Address_(geography)
Also mandatory zip codes. I keep getting sites that won't let me submit a form without a zip code, even after I've deliberately chosen Ireland in the list and the page refreshed and replaced the state field with a county field. The latest case where this happened to me was creating an account on Sony's website for the Planetside 2 beta. I usually enter in na or n/a for that, but I've even had sites that attempt to validate the zip code according to US rules even after I've selected Ireland in the country box.
(For anyone wondering, post codes in Ireland don't exist outside Dublin, and even then they're a number from 1-24, which doesn't validate either)
