I agree with mojopixel. Apple clearly have an issue with this. My iMac is currently being fixed at the Apple store. Even though I have noticed some good screens in various stores, there was one amusing moment when I took mine into the store. When I was explaining what was wrong I pointed out the same yellowing on one of the demonstration models in the store, although not as bad as mine. This was just one of the problems, the backlight bleeding was the worst problem.
Apple have ALWAYS been famous for the quality of their screens and graphics. I certainly believe that if you have invested good money in a top quality machine, then that is what you should get, especially from a company like Apple that prides itself on both its hardware and software.
Like mojopixel says, the more people who point out the problem and refuse to accept anything less than standard Apple quality, the quicker Apple will be to fix it.
For myself, I came to the decision that I was not prepaired to sit working in front of a screen I was not happy with for the next 3 or 4 years.