I have a 2011 Scott Addict R1. I just picked it up a month or so ago because I had ridden my previous bike like 6 years only moderately and wanted to really get into the sport with a new, decent bike. The previous bike was also carbon fiber and was a Kestrel Evoke, which is basically a bottom-of-the-barrel starter bike.
I have never had a single issue regarding the carbon fiber in all my riding. Some manufacturers put a weight limit on them, but neither Kestrel nor Scott do. I tried out an aluminum-framed Cervelo S1 that was on closeout when I was shopping for a new bike a couple months ago and I could really tell a difference in the harsher ride because of the vibration. The bike shop said the harsher ride was attributable to the aluminum versus carbon frame.