I would like to add my own experiences to this issue for my 2011 27" iMac. About a year ago I had this problem happen, and I called Apple. The first supervisor said that although my computer was out of warranty, he would see what he could do and that I should ring back. Of course, I didn't get his name or extension so when I bring back I get someone completely different who definitively tells me that this is not covered by anything, and as I am out of warranty I will have to pay. I take it to my nearest apple approved retailer who tell me they can replace the screen for $1000. Half the price of the computer.
Having seen on the internet that this is a widespread problem I ring apple and tell them that I am prepared to take the issue to Fair Trade if they don't replace the screen. I immediately get transferred to complaints who agree to pay for the fix. I save $1000.
And I'm bloody glad that I did because now less than a year on the problem is starting again, and detiorating much quicker this time. This problem is a joke, and apple have really created a lemon with this screen. It is an absolute disgrace that they will not admit that this is a problem given the thousands of complaints they must have got on this issue on this and only this model of mac.
So my suggestion to anyone with this problem is DO NOT PAY for a new screen. The problem will return because they replace it with another poorly made screen. The only way to permanently solve this seems to be:
1) Get lucky and not have a lemon.
2) Keep pressuring apple to give you a new screen every time your new one stops working.
3) Buy a new computer.
Obviously they do not admit this is a widespread problem because they just want people to do 3.
This makes me so angry as I have used macs since 1992. Since leaving school I have bought 3 myself. I see no reason to have to buy a fourth when this one works fine, and I got it just over two years ago.