Randal Archibold of the New York Times offers "Report Questions an Immigration Program That Uses the Local Police" (link):

A government report questions the effectiveness of a federal program, long criticized by immigrant advocacy groups, that deputizes police officers as immigration agents.

The report, to be released Wednesday by the Government Accountability Office, the investigative arm of Congress, says the government has failed to determine how many of the thousands of people deported under the program were the kind of violent felons it was devised to root out...

As he later says, who exactly they're supposed to go after isn't spelled out in the law, although the internal Department of Homeland Security policies are to go after smugglers, violent criminals, and so on. The GAO says the DHS didn't make that policy clear, and their report includes a reply from DHS saying that they're making changes. Archibold's report also references Joe Arpaio's efforts and the report from Justice Strategies; he calls the latter George Soros-linked group "a nonpartisan research foundation".

Rep. Bennie Thompson will be holding a hearing today. More as it becomes available.

UPDATE: The report is available here; if anyone reads it leave notes in comments. Stock comments from Ali Noorani of the National Immigration Forum and Angela Kelley of the Immigration Policy Center are at: lawprofessors.typepad.com/immigration/2009/03/congressional-h.html