This is like a bad chain letter. It seems to be affecting the UK mostly. There is some real bad information going around that seems to Target Mexico every year. (Swine Flu Last Year), The truth is that Mexican Banks themselves are no longer going to operate using US Dollars. Also, are limiting USD Money exchanges to prevent laundering from Drug Cartels since they deal in USD mostly. The first bank to do so was HSBC, then Bancomer followed, along with BanNorte. This does not affect the Tourist at all unless you walk into a bank, stand in line and want to change dollars. Why do that when you have an ATM attached to the bank and you can get pesos without hassle. if you Google "Mexico to stop accepting US Dollar' You will get other forums pointing to an article in the El Universal stating that Banks will stop accepting US dollars to curtail Cartel money. It does not state anywhere that Mexico as a Whole Nation, from the guy selling necklaces on the beach to the local shops and restaurants. This some real bad information, and it only makes money for the overseas exchange companies take advantage of worried tourists to use them to change money and get a crappy exchange rate.
Here is basically the only article on this issue. It is in Spanish.
The first paragraph translated states that "The Banks Themselves decided to limit US dollar Transactions"