I have broken two on different road bikes in the past two months. My weight fluctuated between 185-195 during this time. I have never tried carbon posts on my MTB's.
These are the posts I have destroyed
1. Sworks carbon with the PAVE insert cracked at the rear seat clamp.
2. OEM that came on a 2004 allez comp. cracked at seat clamp.
never again. can you say thomson?