I spent 12 months commuting on a carbon bike. It's perfectly doable, but it has its limitations. The biggest limitation for me was carrying capacity. Carbon bike = no rack mounts, which meant I had to carry everything in a backpack. Even carrying only the essentials, it was tough going. If I ever had to travel to town (instead of to work) it also meant carrying a change of clothes, toiletries, shoes and usually study guides and the like. That was a much heavier load to carry and I'd usually wind up with bruises around my shoulders and armpits from the shoulder straps.

12 months on, I've bought a bike just for commuting - an alloy road bike with rack & panniers. I love it. It lets me carry a reasonable load (instead of bare bones), and is much more comfortable. That said, if you really want to commute on your carbon bike, do it. If you can tolerate the load on your back over the distance you're doing, just do it. You'll like it better than driving, I guarantee.

Max