Bloomberg Television interviewed Department of Homeland Security Secretary Janet Napolitano today, and she said among other things (link):

"It is fair to say there are individuals in the United States who ascribe to al-Qaeda-type beliefs... And so it makes information-sharing, it makes effective law enforcement and it makes the shared responsibility of law enforcement ever so important."

If she's telling the truth and has accurate information, very few of those she's discussing will probably be native-born Americans; most or all will have come here legally or illegally due in part to intentionally lax standards and enforcement.

And:

Intelligence tips on terror suspects are more important than a system to track visitors leaving the country, she said. She also said better border enforcement will help make the case for immigration legislation.

In the U.S., the government has put money into gathering intelligence about the movements of terrorist suspects, Napolitano said. “The key thing is intelligence analysts,” she said.

This effort is more of a priority than developing a system that could keep track of visitors, she said. The government can’t track the more than 200,000 people who intentionally have overstayed their visas, the New York Times said today.

"Such a system would be very, very expensive and laborious to have, given the kinds of border we have,” she said. Scientists and engineers aren’t “even sure they have the technology to make it work."

I'm a bit suspicious of the last; see [1]. Then, Napolitano continued sounding highly similar to her predecessor Michael Chertoff:

In addition to improving intelligence, the U.S. is getting more control over its borders by adding Border Patrol agents and increasing enforcement, particularly in the Southwest, said Napolitano, who was governor of Arizona until President Barack Obama picked her for his Cabinet.

The stepped-up monitoring and rounding up of illegal border-crossers is quelling opposition to immigration legislation, she said.

“One of the things that has changed is that there has been a lot of enforcement at the Southwest border,” she said. “It’s just not the same border.”

[1] From the New York Times (link):

But Homeland Security officials said that a series of pilot programs since 2004 had failed to yield an exit-monitoring system that would work for the whole nation. They have not yet found technology to support speedy exit inspections at land borders. And airlines balked at an effort last year by the Bush administration to make them responsible for taking fingerprints and photographs of departing foreigners. Last year, official figures showed, 39 million foreign travelers were admitted on temporary visas like Smadi's. Using current procedures, Homeland Security officials said, they confirmed the departure of 92.5 percent of them. Most of the remaining visitors did depart, officials said, but failed to check out because they did not know how to do so. But more than 200,000 of them are believed to have overstayed intentionally.