When my carbon bike was put together last spring they routed the front derailer cable wrong. Under the bottom bracket is a hole that the cable is supposed to run through. They didn't run it through that hole, and as a result there is a slight (very slight, but visible because of the colour and your nail catches it) groove in the carbon.
I've talked to the bike shop who takes full responsibility for it, and the manufacturer is now involved. I emailed them pictures yesterday and I'm concerned they will say that it's a minor groove and not structurally an issue. I hope they won't, but you never know.
I've attached a picture of the bottom of my bike, and I drew a very professional arrow to the groove.
I've read that carbon is super weakened by any breach in the body. I don't want to get into a carbon sucks thread, but I'm curious about a) whether this is a serious issue and b) because of where it is, if they don't honour a warranty claim and I don't feel like going to small claims court, then is this still safe to ride?