Immigrants are good for business. In fact, the rapid clip of U.S. economic growth might not be possible without them. Even as academics debate whether immigrants take jobs away from domestic workers, and as homegrown militias organize to patrol the nation's southern border, hundreds of thousands of immigrants -- more than half of them undocumented -- make their way to jobs in the United States every year. According to the Census Bureau, more than 80 percent of the foreign-born population, estimated at close to 34.2 million in 2004, is of prime working age versus only 60 percent of the native born. This figure includes more than 10 million undocumented migrants -- an all-time high, according to a Pew Hispanic Center report from this year.