To save you a ton of research, prior laws already state that you must have ID on you at all times. This new immigration law does not give ANY authority for PO's to pull over somebody if they look like an immigrant, it only pertains to people who are already in police custody, or being questioned.
And I ABSOLUTELY LOVE hearing on the radio that people are moving out of arizona because of this. That is great, the law is working. Now if the other 48 states pass this (Utah is passing it right now) we will be much better off.