It was used last night in a debate by Michele Bachmann. Many people hadn't heard it. Here's the wikipedia entry:
"Anchor baby" is a pejorative term for a child born in the United States to immigrant parents, who, as an American citizen, supposedly can later facilitate immigration for relatives.[1][2] The term is generally used as a derogatory reference to the supposed role of the child who automatically qualifies as an American citizen and can later act as a sponsor for other family members[2][3] The term is often used in the context of the debate over illegal immigration to the United States, but is used for the child of any immigrant.[1] The practical immigration benefit of having a child born in the US is disputed; family reunification (family-based immigration) in the United States is a lengthy process and limited by law to categories prescribed by provisions of the Immigration and Nationality Act of 1965.[4]

