[2000neon]

The first example that comes to mind was the 1970 Dodge Charger Daytona/ Plymouth Roadrunner Superbird. The street cars had fake ducts, but the real race cars (and apparently some early street versions) had real, rear facing vents on top of the fender which vented high pressure air out from the top of the tire. Supposedly from what I understand is that they decreased lift and helped with high speed (200 mph) stability.

Also, there must be something to having a smooth, clean exit from the wheel wells in terms of fuel economy, look at the first gen Honda Insights. MetroMPG just recently posted some video of a tuft test he did in that area which shows clean flow out of the wheelwell, which drastically reduced turbulence along the edge of the car.

I suppose you could also use an air vent to aid as an exit for ducted air through the radiator. That way you don't have the issue of creating turbulence by venting that air into an area of attached flow, since the area within the wheelwells is already so turbulent.