One thing you have to be very careful, just read about this on flyertalk, is absolutely never let a foreign country cashier charge your card in US Dollars.
Several of the members on that other board mentioned that when they would stay at hotels, restaurants, and the like most of the time the cashier or clerk attempted to charge their card in US Dollars. The currency exchange rate on those dynamic currency conversions (DCC) is very unfavorable. You get a much better deal by paying in local currency, and even more a lot of banks will use the best rate on the days from the time you made the charge, until it cleared.
Of course when they complained and asked to be charged in the local currency, the cashier tried to talk them out of it saying it was "For their convenience" to have the charge in US Dollars. Not true. Since running the charge in US dollars gives the customer an unfavorable exchange rate, it is only better for the merchant. The US dollar charge might also have a foreign transaction fee apply depending on the bank issuing the card.
It is also a violation of the Visa or mastercard agreement to force a charge on a customer in one currency. When traveling international you must be given the option to pay in local currency.
Always pay using local currency on your card when traveling international, you always get a better rate.
