I too have had the fullscreen brightness flickering. My screen also looks lightly milky sometimes, like a light blue-gray even fog, mainly when I return from screensaver.
I've needed the MBP to do work, so I haven't returned it. It's just visible enough to be annoying. It doesn't flicker that often, but it shouldn't at all! I certainly won't let my warranty end with this screen issue still occurring.
The first time I noticed it was the first time I switched to the Nvidia9400 to conserve battery. The brightness level changed and then started a subtle, fast flicker. Now it seems to happen randomly at different brightness and video card settings.
My screen isn't flickering at the moment, but it does when I view this test:
http://www.csse.uwa.edu.au/~lucas/background.html
Well, at least the image in the browser flickers - not the whole screen like usual.
My 2003 Toshiba doesn't flicker when I view it there. Its screen has always looked great.
Don't even get me started on all the other issues I've had with this late 08 MBP, Pro Tools 8 003 Rack and a OWC Mercury Elite Pro drive... it's been so frustrating.