van cough, read this http://www.singletraction.co.uk/?fn_mode=fullnews&fn_id=105 I wouldn’t worry too much. Just to add to that write up, Sam has recently bought a NEW 2009 MagicLink Kona Coilair (their super tough 35lb AM bike) and managed to break the chainstay within a few months. His very early generation carbon bike lasted nearly 20 years.
The only concern I have with carbon is if it takes a hard hit from something like a sharp pointy rock. With alloy it would most likely just put an unsightly dent in the frame, with carbon, it might punch a hole in the frame.