ive had 2 cars now with CF vented bonnets, R33 and now R34, both fine, no probs at all, as someone else said, the vents are usually positioned in places which wont effect anything, both of mine have had the big vent in the middle between the radiator and engine so the water runs staight out and the side vents have been close to strut towers so neither really allow water to touch anything but the car body, only issue that i noticed was that on the od occasion i would get a little bit of fanbelt squeek due to the water, but it only lasted a second or two....... hope that helps