The Arizona immigration case decided yesterday at the 9th Circuit. It was decided on preemption grounds. Immigration enforcement is a matter of federal law. States cannot devise a mish mash of separate laws to suit themselves in violation of a federal statutory scheme. The Arizona law was declared facially unconstitutional.
You can read the entire opinion here: www.ca9.uscourts.gov/datastore/general/2011/04/11/10-16645_opinion.pdf
Or at the 9th Circuit homepage here: www.ca9.uscourts.gov/