[aerohead]

Originally Posted by MetroMPG

Interesting. I didn't come to the same conclusion, but it's hard to tell from the stills I have. FYI, there are pics of the smoke testing of the car in this thread: Wind tunnel images of GM EV1 (Impact) and Sunraycer solar car

My thought is that with attached flow,the smoke would lay directly against the surface of the backlight and close to the trunklid right to the end.
Your wind tunnel image ( thanks! ) and my still clearly show the smoke trace far above the body,indicating a captured/locked vortex,with flow separating up at the backlight header.
It's been mentioned in the press,that GM has very stringent and rigid standards for outward visibility which may lead to aero compromises.