I took my MBP C2D into my local Apple Service Centre ( it's not an Apple store - it's an Apple Premium Centre - they're very good there), anyway, I had 2 of their technicians look at the screen. They brought down a 2.16Ghz MBP C2D to compare my 2.33 against.
Their screen showed the same grainy effect, although it wasn't as noticeable, as their screen on full brightness was at the same level my MBP when it's on 6 bars brightness level, so their screen was much duller.
At first they couldn't see what I was talking about, both techs said my screen was amazing. After about 45 minutes, one of the technicians said "what's that on the screen". I asked him to elaborate and he said it's a sort of grainy shimmer effect on the screen. (Bingo! I thought at long last) he then looked at his own MBP screen and said it was on his too only not as noticeable.
The second technician only saw it when I set the background to a solid colour, he said it was as if the screen was moving.
So, it only took best part of an hour of constant looking at the screens for the technicians to both agree there was something odd about them.
They offered to replace the screen, but said they didn't see much point until they investigate with Apple the cause of the issue. I tend to agree with them in that regard. They know of the problem now so when they come up with a suitable fix, they will get in touch. Both agreed the MacBook has a better displayed image than the MacBook Pro - I responded "when the MacBook is primarily aimed at stoned students and the MacBook Pro is aimed at professional creative sorts who need a high quality display, why would the stoned out students get the better of the two?" Both techs laughed at my analogy, but agreed it made no sense that the MacBook Pro has such a lesser quality display than that found in the MacBook.
So, my advice, if your screen is grainy, take it into Apple or an Apple authorised service centre and take as long as it takes for them to see the problem. Show them on a solid light grey background, that's what showed my screen at it's worst, and they can't fail to see it. If they do, they're either blind or lying.
Only when a high number of service centres get in touch with Apple, will they (Apple) start looking into the display issues we're experiencing.
If Apple do nothing to resolve this matter, I think that shows clearly what Apple think of it's customers, in which case, direct action is required, i.e. arranging a specific day and time, where we all march upon our nearest Apple Stores or resellers, MBP's in hand and demand action. I think if several thousand people around the world turned up to complain about their MBP displays, Apple would have to take notice - especially if TV media was involved - think of the bad press so close to the holidays!