I think the holiday firms really need to get their act together with this one and confirm the correct information as soon as possible. We are due to fly out to Cancun on 1st October and the first I heard about this was on this forum from the comment from Denny53. My mother and father in law were flying out to Cancun on 3rd September, and they received a letter from First Choice on the 2nd of September stating that they could no longer use US $ in Mexico and that exit tax etc had to be paid in Pesos or Sterling. Luckily it wasnt too bad for them as they had exchanged Sterling for Pesos before they went (and not US $ or that could have been a nightmare).
Following that, I waited to see if I would receive a letter from First Choice confirming the details. Still nothing yet and we leave for Mexico in 2 weeks time. We went into the travel agents on Saturday and asked the question and asked why we hadnt yet received any formal notification (after all - we are just about to order our currency for going on holiday!!) we were told... oh you are on the list, the letters go out 3 weeks prior to your departure date. I still havent had anything from them yet!
Surely they should be sending out a mass of letters to ANYONE travelling to Mexico. Not everyone leaves it to the last minute to buy their currency for going on holiday.