aw this on Fifth Gear and went straight to the web to find out more...
High pressure air from under the car is vented at the leading edge (side) of the tail light assemblies.
Apparently this accomplishes 2 things:
1 - relieves under car pressure, reducing lift and eliminating the need for a deck lid spoiler
2 - interacts with the flow at the transition at the rear of the car in a way that reduces turbulence, reducing drag.
The car has a decent (for modern production cars) cd of 0.27.
More info:
http://www.autoblog.com/2007/02/09/m...ted-taillights
http://www.worldcarfans.com/rsslink....ed-tail-lights