It makes my head hurt when I hear the anti-Arizona immigration issues misrepresented. Federal law states that, "Every Alien 18 years of age or older shall at all times carry with them and have in his possession a certificate of Alien registration or receipt of registration issued to them."
So Arizona is only enforcing current federal statutes. The debate is the process of how to determine when an officer should ask to see the government issued certificate. I'm sure Arizona will get this figured out.