The prepared remarks of Janet Napolitano of the Department of Homeland Security to the Senate Homeland Security and Governmental Affairs Committee are here. Among many other things, she says:

...As infected travelers can lead to the spread of this virus, DHS is taking a number of precautions in light of the scope and nature of the threat... The actions we are taking regarding international travelers match the precautions advised by the CDC and the World Health Organization (WHO) based on the current, evolving epidemiology of the 2009 H1N1 flu virus. According to both the CDC and WHO, closing the border would yield only very marginal benefits; at the same time, closing the border has very high costs. The strain of the this virus that was first detected in Mexico is already present throughout the United States, and there is no realistic opportunity to contain the virus through border closures, so our focus must now be on mitigating the virus. The actions we are currently taking, as well as the travel advisories issued by the CDC and the State Department against non-essential travel to Mexico, should help to mitigate the number of people infected with 2009 H1N1 flu crossing the border.

Those would seem to be in conflict. During the questioning (link):

Napolitano said that "passive surveillance" is "not an accurate picture of what is going on" at U.S. entry points. She had used that term Tuesday morning to describe the nature of the monitoring for illness.

On Wednesday, Napolitano said that U.S. officials are "actively" questioning visitors at the border, asking questions about "whether they are ill, their travel history and the like."

That contradicts eyewitness accounts here and here.