Hi guys, here is my experience:
Bought my first Macbook Pro Retina in February 2014 (15-inch, 2.6 GHz, 512GB, German keyboard layout). Till today I havent found a single good screen.
I am currently using a Macbook Pro 2011 (non-retina, non-glossy) with an LG Screen that looks amazing in color and contrast and backlight strength.
I went through nine Retina machines all together. They all shipped directly from the chinese vendor to the US. I had amazing help from a shopping assistant at Luvocracy that dealt directly with Apple and took care of the shipping and re-ordering process. Apple sent me a pair of free headphones after the 7th bad screen. I also once had a phone call with a lead service representative at Apple and he pretty much admitted that Apple has no control over the quality of the screen and that this is an ongoing issue.
The main problem is certainly the wide variety of image quality you receive on those screens.
The Samsung screens tend to be more uniform in their backlight support. Sadly they come with a more yellow native-white coloring that makes them hard to be used for graphic design. Grays turn out to me more brownish and reds more orange. You cant really fix this problem by using an external calibration and measuring device and creating a color profile (which I tried). The native white tone cant get any whiter (in this case less yellow) than what the screen offers.
Most of the Samsung screens varied widely how intense those yellowish colors appeared. Some of them were terribly yellow, others were not uniform and more yellow in the top or bottom parts and should in my opinion not be shipped out to customers.
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non-uniform Samsung screen. Notice the different grays that look brownish in different areas.
Two of them had LG screens that seem to have much better native-whites. Sadly one of them had a purple area on the top left and a yellowish area in the right bottom. Both did not show any kind of image retention so I assume the latest LG screens (late 2013) dont have this issue anymore.
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non-uniform LG screen with strong purple on the top left part and yellow tint in the bottom right area.
The most perfect screen I received was actually an LG screen. Sadly Apple messed up my order to include a 3D graphics card in that Macbook and I had to return it again. It was sad because that screen was truly amazing looking and totally uniform.
I do recommend the LG screens if they are uniform. The whiter native-white ensures better calibration options.
After my 9th return Apple did not allow anymore exchanges and offered a repair instead. I declined since it makes it impossible to return the machine with a full refund in case Apple installs another yellowish Samsung screen that might be ok by their standards but not by mine.
As other folks have described it the problem comes down that you dont have the option to select upfront an LG or Samsung screen. It also doesnt look like there is any good quality control happening on Apple's side in regards to screen quality.
I would not recommend at this time to buy a $2700,- Macbook Pro Retina. Especially if the screen costs more than one grand and is supposed to be the killer feature and big reason to buy it. The Retina display reduces glare while maintaining incredible color and quality. - I may disagree with that statement.
Please let me know if you have any questions.