It really all depends on where you are and what card you proffer.

If you book with a US credit card that carries forex fees, you will pay - usually 3% extra. But use a credit card free of such frippery - Capital One, some AMEX, etc. - and you are rid of these nasty bloodsucking fees. And yes, booking and prepaying on HH in the US for a foreign property will generally still incur forex fees if you are subject to them.

That having been said, Australian hotels will hit you up for credit card usage fees as well, even if you have a non-forex fee card. Oh, yeah, they accept Aus dollars... The dilemma in "Godzone" (AKA Australia, Oz) becomes "do I use my Surpass and pay 3% surcharge PLUS the property's credit card usage fees, or..." So, Andriyko's post holds up in most places, but not all...

Some properties will offer to bill you in your home currency (Dynamic Currency Conversion) - you will the, if you are really unlucky, pay the forex fee and pay at the property's skewed exchange rate and you will really feel aggravated when you see this on your credit card statement.

Be aware - booking travel with foreign airlines and cruise companies can incur forex fees - e.g. the fact BA has US offices makes no difference. And some travel providers offshore bills processing, so even though it looks like an American company and has an American address, you get stuck again with forex fees. These are lucrative to credit card companies, so figure how you can evade them. "What are you putting in their wallet?"