I made a practical but unplanned test of the "Gorilla Glass" Apple uses for the iOS devices. I was helping out with a local Memorial Day parade and I foolishly brought along my iPad in case of "downtime" before the parade started (there wasn't any, and I should have known better, but it's been a couple of years since I helped out). While trying to direct traffic and handle some radio messages while running back and forth in the parade staging area (where the floats and marchers all line up before heading out), I dropped my iPad onto the street. Of course it landed face down, and of course the magnetically-attached Smart Cover fell off on the way down.
I thought for sure I had just totaled my iPad. But I picked it up and didn't even see any damage! It was working just fine, and looked no worse for the wear.
Today I took a closer look, and I can see where I definitely cracked the glass:
Now, I had to tilt it just so and turn on the flash in order for this to show up so nicely in the photo. To the naked eye, you have to know where it is in order to find it. In fact, I had trouble finding it when I knew it was there.
Fortunately, there is no damage in the section of the glass where the screen is, so I was very lucky. I don't recommend this sort of torture test – but it's good to know that the device is robust enough to take a beating.