Visiting Mexico over Christmas, I found that I never once needed pesos. The hotel, for example, offered snorkeling trips to the Palancar reef. The price? $80. "How much in pesos", I asked. We'll have to multiply by $11.80", I was informed. In other words, the price was in dollars; the peso price would have to be converted.
Even the Mayan street vendors outside Chichen Itza quoted prices for masks and fabrics in dollars.
I went to a local shop to buy stamps and I was immediately given a 80-peso stamp. "Unless you are from Europe," trailed the cashier, "then it is 105 pesos." Those apparently were the only two choices -- United States or Europe. The possibility that I might be mailing a local letter didn't even arise. It's just that the Yucatan econonomy is organized around tourists.
The really ridiculous thing is that the daily usage fee that the Mexican government charges to go into protected marine areas was quoted in dollars -- the peso rate would vary but the dollar rate was fixed. Even the Mexican government would rather take dollars than pesos!