The WHO has updated its pandemic alert level to 4, meaning that the virus is showing a sustained ability to pass from human to human and is able to cause community-level outbreaks. The WHO has not changed its recommendations about travel to Mexico:
"WHO advises no restriction of regular travel or closure of borders. It is considered prudent for people who are ill to delay international travel and for people developing symptoms following international travel to seek medical attention, in line with guidance from national authorities." - WHO Web Site
Mexico City is at a stand-still with schools, museums, theaters, and other institutions closed, and the mayor has said that if the situation worsens the entire public transport system will be shut down. All schools in Mexico are closed until May 6 in an effort to curb the spread of the swine flu virus.