Officers will not allowed to pull anyone over because they "look illegal." Just like with AZ's current seat belt law- there must be a valid reason to pull someone over or talk to them BEFORE you can question their legality. Cops will not be just walking around bugging every tan skinned individual.
as for the "reasonable suspicion" used to asked for further id, a number of things could fall into this category:
license plates from out of the country, inability to speak English, lack of proper id (drivers license, insurance, registration,) 16 people crammed into a Kia Sportage, etc.
See this post: http://Off Topic Forum.com/topic/29146-arizona-state-senator-responds-to-immigration/page__view__findpost__p__105950
then what are you still griping about???