I disagree. This is the only forum where you see people posting pictures of their screens asking "I don't see any yellowing, but can you tell where it is" type of questions. Amazon buyers rate both the 27 and 21 iMacs with stellar reviews, as well as multiple awards the computers have won for design and operation. The paranoia tried to lend itself to iPad screens as well, but it didn't hold.
Like I said before, all screens are not perfect, and if you get one that is off, you certainly should get a replacement. However, there is a reason why this kind of thing does not exist with LCD televisions, due to the fact of those manufacturers not allowing it to happen. If returns were always specifically up to the buyer's preference, either prices would be much higher than they are, or many would go out of business. Apple will get to that point as well, and it will just make it harder for those with legitimate claims to get satisfaction.
One guy said he exchanged his 9 times. Give me a break.