This is a bit of a misleading question as out-right catastrophic failures are rare.
The better question for carbon frames (and components) would be how many carbon frames have:
- a crack down the seat tube
- a crack on the top tube
- a crack on the down tube
- a crack on the bottom bracket
... all this in many cases where the onwer doesn't even realize it what might have caused it until he happened to discovered said cracks by chance
all these sort of cracks, while not catastrophic failures, are effectively causes of concerns for failures that the owners will have to fix them to have peace of mind
- what about cracked stem due to overtightenng?
- what about cracked carbon handlebars from a simple bike tipover?
- what about imperfect finish, ie., the dreaded "wavy" seat tube or down tube due to crappy molding process?, or the "bubbly paint'?
A buddy had his Specialized fork broke cleanly at the steerer tube while he was riding at ~20 mph on good pavement, but that was enough to send him to the ER room and spent a few days in the hospitals with a busted up face. He quit cycling after that because his wife made him.