A while back I ordered some small PCBs from a domestic supplier that fit in a standard envelope. They arrived with a bow in them. I contacted the Ebay seller and he knew exactly what had happened and was pissed that USPS had not processed the letter as they should have, given the method he had paid postage for. Apparently, depending on service, the letters run through rollers which put the bow in the board. This sound familiar? I may need to ship some PCBs and would rather not have to box them up so they don't end up warped.