Keep reading responses similar to those above - my experience appears to be a bit different.
I'm a fan of being able to spend, but not a fan of traveling with lots of cash. Travellers checks were accepted everywhere we wanted to use them last year - this year we didn't bother. 2 of us arrived with less than $400.00 us total in cash for a 9 day stay.
Everywhere I wanted to use my AMEX it was accepted (Except the water taxi & they took Visa). I can think of only two places who charged extra & I'm not opposed to the merchant passing the extra fee on to me, the convenience and frequent flyer miles are worth it. (Even offered to pay extra on one occassion, but was turned down and assured it was no big deal.)
The 24 hour ATM worked fine with my american ATM card even on weekends, was never out of cash, and fee was no worse than that charged in the states when I go to a bank other than mine.
Charged the ruins trip & golf cart rental to our room - breakfast each day was included w/ the room - credit card for big dinners and the furniture we bought - cash covered everything else.
Matter of preference - cash or credit seems to get you by.