The thing that I see bad about the CF trunk is that your car as a FFD setup, the front/rear weight ratio is already extremly basis toward the front. Taking weight of the back will just further this effect. For Drag, it would not be a bad idea but for handling, it is not as funtional.
2 bad parts about CF that I have seen/think.
One, they take away from the whole sleeper look and the unpainted are played out. The Eclipse on FnF made it popular
The clear coat on them sucks. I have seen a few cf hoad look like they have been sand blasted due to road elements.
Painted is the only way to go. On inlinefour.com, there CF hood brand has a link on there page. They have a vid of a car running over a CF hood, returns fine. Another one is of a person jumping on one. Acts like a trampoline.
Only safty concern I have heard from them is that they are TOO strong in crashes sometime and instead of bending/braking, they just get pushed back and you will have the edge go flying through your windsheild and could possible make you a turn from 6 ft to 5 ft 2 inches real quick.