This month the Department of State issued an updated travel warning for Mexico.
(From the Department of State website) February 08, 2012 - The Department of State has issued this Travel Warning to inform U.S. citizens about the security situation in Mexico.General information on the overall security situation is provided immediately belowFor information on security conditions in specific regions of Mexico, which can vary, travelers should reference the state-by-state assessments further below. This Travel Warning supersedes the Travel Warning for Mexico dated April 22, 2011 to consolidate and update information about the security situation and to advise the public of additional restrictions on the travel of U.S. government (USG) personnel.
Cnn.com summarized the warning:The travel warning urges Americans to defer nonessential travel to all or parts of the following 14 states: Chihuahua, Coahuila, Durango, Nuevo Leon, San Luis Potosi, Sinaloa, Sonora, Tamaulipas, Zacatecas, Aguascalientes, Guerrero, Jalisco, Michoacan and Nayarit.
Travelers should also exercise caution visiting all or parts of Baja California, Colima and Morelos, it says.
Here is detailed safety information on Travel in Mexico from the Department of State.