Back when my whip was a Volvo 740, I ventilated my taillights, too. Actually, it was more like drilling drain holes, but once all the trapped water escaped, you can bet that the compromised seal allowed plenty of air to flow through the lamp. Mercedes has applied intelligent thought to using the taillight as a hidden aerodynamic diffuser on the new C-Class, resulting in a slick Cd of .27. Instead of marring the design with some kind of tacky, nasty lip spoiler on the trunklid, the aerodynamic wunderkinds at MBZ have applied some clever trickery to keep the arse of their newest kostspieliges auto looking slick.
A lip spoiler changes the airflow behind the vehicle by interrupting the smooth flow coming over the top of the car. That interruption reduces lift. The problem with a spoiler, is that they require a specific shape to attain their spoiling effect, dictating styling direction. The C-Class engineers have taken an alternate route to addressing the vortices out back. The taillights act as diffusers, pulling air from underneath the vehicle and venting it out of slits in the lamps. The high pressure air under the car now has somewhere to go, which reduces lift. An elegant alternate solution that achieves the same result as the old spoiler. The air coming out of the taillight lenses also affects airflow along the sides of the car for the better, keeping turbulence behind the new C-Class down. We can't say how close you'll have to ride your bicycle to this thing to get sucked along by the bubble, or how badly it'll mess up your hair when it passes by, what with all that air blowing all over the place, but it sounds like a clever trick.