I had and still have the yellowing effect with my iPad. I left it on a white screen all night in a drawer with brightness on high. It seems to have helped a little, but as I type this with a split keyboard in portrait mode, the left portion if the keyboard is obviously more yellow then the white right side. Oh well, it was worth a try and it's going back tomorrow.
The most obvious way to tell if it's still a problem for me is flipping it upside down. I showed my mom yesterday and in normal portrait mode she didn't see a problem, but when I flipped it with the home button on top, she saw it.
Just adding some thoughts to the discussion.
It wont help at all, its an issue with hardware, leaving the screen on full brightness overnight is likely to cause more problems than it resolves.