Hello:
I see the grain too. I don't own one, but I picked up on the grain right away on a display model at a store. I have owned many, many powerbooks over the years and have a good stock of experience upon which to compare the MBP C2D 15.4" screen to. The screen is EXACTLY LIKE THE POWERBOOK WALLSTREETS. The Wallstreet has a grainy screen too. It is really pronounced when placed beside a PowerBook G3 Pismo. The Wallstreet was the first Apple laptop to have an ATI 2D/3D graphics card: ATI Rage 4 mb. The graphics card in the Pismo is an ATI rage mobility (8 mb).
Nobody has ruled anything out, including the graphics card being the possible problem. Or, it could be just the matte screen/pixel density, or a combination of all of these.