i have done it. i have a cone filter where the stock flat panel filter is. took all the coverings for the hood scoop off. so, in away, i have a cold air ram intake. i only put a cover back on during winter. i don't want water to get in there.
The only problem with making the hood scoop functional is water getting into the intake.
So if you live where it rains, it is a bad idea.
There was a post of a guy trying to sell his buddies home made ram air intake, and he claimed to have no problems even in a downpour, but from what I have read, water will slow the rate of burn, (water injection is used sometimes in really high compression engines, kinda like using higher octane), and in a car that is designed for a specific rate of burn (octane 87), this will lead to incomplete burn, thus loss of HP.
It's always a good idea to get the heat out from under the hood. I did some temp readings at 6 locations under the hood and saw that the box off of the throttle body will get heat soak and raise the temp some. I cut the blocking plate in such a way that it will let air in to cool but not let in water and dirt for the most part. The hood vents are blocked too but are there to let heat out. Teh hood scoop forces it in and it comes out the vents. Although others haven't had problems with rain water getting on the motor from the scoop or vents I made it so heat can get out of the vents w/o the water problem. I just like to keep my motor clean is all. The best place to grab air is from the fender, it's the coolest air.