When I had mine, the senior adviser basically said it's acceptable behavior for that "vintage" of Macbook Pro, and the workaround is to use the 9600GT. When I heard that, I got the feeling they had _no intention of fixing it._ The unit was finally exchanged (for other issues, not limited to this) but my current one (i7) hasn't been without issues (mainly build quality) yet strangely no flicker/flickering like the previous late '08 model had.
Here's the link to my flickr page if you want to see the video I sent Applecare at the time. I never managed to get a video of black bar across the top of the screen but did capture the fluttering backlight.
http://bit.ly/etrchK
In the end, I threw in the towel and picked up a Lenovo.