Funny you brought this up; I had just been looking into these a few weeks ago.
Here are a couple more pics I came across:
Aside from the clearance issue (had one on a Mini, and you get used to the limitations pretty quick), my main concern would be drag. How much is the car affected/improved/hindered in daily hwy driving? Handling? Cooling? How about mileage? I would love to hear from anyone who has installed one of these...
EDIT: FYI on my Mini, I noticed no real difference in handling or fuel mileage, but did feel a little drag accelerating up to speed. I did have a major improvement in cooling at speed, the dam being ducted to the radiator, and as that was my goal, I was happy. No speed-bumps for me, though...