The information above is not accurate. You will still be able to make purchases up to $100
using U.S. Dollars. This will have little impact on the tourist areas.
As always, it can be a good idea to use an ATM and have a few pesos in your pocket for small purchases.
Here is a link to a couple of stories that explains the situation.
Mexico putting limit on purchases in dollars : News : ValleyCentral.com