I actually had a 2 night stay, first night postpaid and second night prepaid (I added on the second night a few days prior to arrival on an spg hot rate).

I used my no forex fee card when I booked the prepaid night through the SPG website and the reservation confirmation showed the price in euros.

Upon checkin, I gave the same card to pay for the first night and was told the second night was already taken care of. Checking out I received 2 separate folios, 1 for each night, each displaying rates and totals in euros. I forgot to ask I be charged in local currency (even though it should be the default...), and when reviewing the cc receipt later, I saw I was charged in USD at a rate of 1.285/1 when the actual rate was 1.24.

I then checked my online credit card statement and saw the the prepaid night has posted at the same 1.285 exchange rate (with no option to ever elect to pay in euros). I don't use my spg amex overseas to avoid the forex hit, but that was completely negated by the DCC charge on two fairly expensive hotel nights ($300-400/nt).

It's annoying to get stung by it on checkout (I'm usually diligent), but to charge effectively a 3.6% markup on prepaid rates with no notice is unacceptable.