In the 17+ years that I have been in the US, I have been asked to show my green card only thrice (I'm not counting airport immigration etc. where you know you need your passport):
- When trying to get a driver's license in Oklahoma in 1995 (long before the "new" law that everyone made such a fuss about). I didn't have it with me, so I went back a few days later with my green card and got the driver's license.
- When returning from Big Bend National Park. Big Bend is far away from the nearest town and right on the Mexican border. When we were coming back from the park, just before we hit the town, we were stopped by the Border Patrol. We did not have our green cards on us (in clear violation of the law!), and this time home was 1000 miles away. The officer called in our driver's licenses and then let us go. Total inconvenience: 5 minutes.
- At airport security when I showed up with an expired driver's license. "Your license is expired," I was told, "do you have some other form of government id? Your passport or green card?". I didn't have either. So, I was frisked and then let on the plane. I came back to Norman and promptly got my license renewed.
I never carried my green card because the risk of losing it was much greater than the chances of being asked to produce it. And as you can see, each time I was asked to show my green card, it was a reasonable request. The first time was state law -- I should have known that I needed proof of legal residency and I didn't. The second time was iffier -- I hadn't crossed the border of the US even though we were on a road that was probably heavily used by smugglers. Whether we'd have been asked to produce a birth certificate or passport if we were white, I don't know. The third time, the TSA officer was trying to be helpful.
Like the Oklahoma law (this is what I wrote when that happened), the Arizona law doesn't really change anything. The law remains what it always was. It's just one more thing to mollify the zealots and rile up the others.