We will be travelling to GSP in October 2011. Here is what my travel agent said about currency:
The Mexican Government recently passed a law that went into effect across the country on September 14, 2010. The objective of this legislation is to limit and control the movement of USD CASH within Mexico. Travelers need to be advised that USD CASH will no longer be widely accepted everywhere in Mexico As of September 14, 2010, here are the more noticeable restrictions to the use of USD CASH to make purchases in Mexico:
1. Hotels and money exchange booths will only be able to change a maximum of $1,500 USD CASH per person per month into Mexican Pesos. Previously there was no limit.
2. Businesses (including Amstar DMC in Mexico) will only be able to accept a maximum of $100 USD CASH per transaction â€“ but the number of transactions per customer is not restricted.
3. Certain businesses may not be able, or may choose not to, accept USD CASH for any purchases at all. (This could include shops, restaurants, etc.)
For example, if a customer wants to purchase a local tour worth $139 USD per person, he will only be able to pay $100 USD in USD CASH and the remainder will need to be paid in another form (i.e. credit card, Mexican Pesos or Travelersâ€™ Checks).Other payment methods such as credit cards of all types, travelersâ€™ checks, Mexican Pesos, and non-US foreign currencies in cash (i.e. Euros, Canadian Dollars, etc.) are not affected by this new law. (*Note: I was in Mexico in December of 2010, and all cab/bus drivers, food servers, maids, etc accepted USD. But you may want to go to your local bank to order Pesos, or a local Money Exchange.
Hope this helps!