And not just for currency conversion, either.

I only use my credit card here in hotels, and since I am nearly always at SGS,.... IME they run the credit card and give you a receipt showing the amounts in THB and USD, as well as the conversion rate (which one could also calculate, of course, on a calculator). Then they ask your preference for the currency in which you'd like to be charged. Seems to work fine for me; but, as I said, my experience is fairly limited. More recently I've been paying in cash (THB). Don't care for the credit card foreign exchange fee on the SPG AMEX.