The NY Times reports that a traveler to Cuzco, Peru, visited some Inca ruins, and found that he couldn't slip his credit card between the huge stones of the anncient walls. Obviously, the problem was that he was using his Amex card. Because the Incas did build great stonewalls, but they didn't take American Express.
(And just what was he trying to pay for by inserting his card in some ruins, anyway? Whatever it was, it must have run out after 500 years, or at least gone bad.)