I've got long personal experience of riding carbon fibre bikes - my first all-carbon frame and forks was bought in 1988 - and my partner Sheila has put in more miles than most, her last 4 PBPs have been ridden on carbon frames, and most of the SR series in between of course.
I've experienced two breakages, both of which were glue failures (ie at a joint between two tubes) and neither of which were catastrophic. I've had similar joint failures on steel frames. I'm overweight, and I now prefer to ride welded Alu frames.
In terms of lifetime - Sheila had one all-carbon bike which was bought in 1992, in recent years has been her '2nd' bike and so used for loaded touring, we finally decided to decommision it this winter, after it had received several nicks and scratches when thoughtlessly leant on a rock last summer. But it was still ridden, with luggage, for the remainder of last year.
So that's 18 years inc 3 PBPs, summer use but high mileage, often with touring loads. She is quite lightweight of course.
I've never seen a broken carbon tube apart from under demonstration conditions. The only tube failure I've ever personally experienced was Alu. Now that was spectacular.
