It did this without me dropping it. It was in my pocket and in an Incipio Feather case. I pulled it out to find it shattered all around the camera. Thankfully a few minutes at the Apple store and $29 later it was sporting a brand new back. As I thought about it on the train home it started to make more sense.
Squaretrade sent me a refurbished replacement for my defective iPhone 4 a few months back. I was positive that their replacement used 3rd party glass for the front and the back. There was no oleophobic coating and fingerprints were extremely difficult to wipe off. Something also felt different about the glass. I put an oleophobic screen protector on the font. It scratches a lot more easily than the glass but it also only takes a swipe of the shirt to clean. There was no such solution for the back. Now that I have a true Apple back again, I realize what a big difference there is. I really think the glass shattered because it was cheap knock off replacement part used by Squaretrade.
All this can be summarized by saying, don’t buy a square trade policy now that Applecare + is available.