Hello, first time poster here but a long time Apple user. I just wanted to share my experience in the hopes that it adds some clarity.
I bought two retina macbooks right when they first came out. One I bought from the store and the other I had built to order. I used the store bought laptop for a couple of weeks before the built to order laptop (with more memory) arrived. I never had any issue with image retention on the store bought laptop at all. When I received the built to order laptop I gave the store bought laptop to my brother.
After a week of using the built to order laptop I noticed the image retention problem. At first it was faint but over the next couple of weeks the problem got steadily worse until an image only needed to be on the screen for a few minutes and the after closing the window the after-image be quite visible and clearly noticibly to even other people for several minutes. For images that were on the screen for a very long period of time (such as the dock icons) the after image would be extremely bright (relatively speaking) and even readable. I googled the problem and found all of these threads. Until I googled I had never heard of this problem so it is definitely not a case of my seeing the problem only because I had read about it first. In other words, it's definitely very noticible even if you're not looking for it. I read about finding the panel manufacturer using ioreg so I tested and found out that my new laptop had an LG panel. I called my brother and he tested the store bought laptop and it has the Samsung panel.
I called Apple Care and they had me take the laptop to an Apple store to have a genius look at it. The genius was able to immediately see the problem. The problem was very clear and he did not need to look closely at all. Even though the laptop was past the 14 day return window Apple offered to allow me to return or exchange the laptop. I chose to return the laptop so that I could order a new one with a bigger SSD and the faster processor.
When I received the new laptop I ran the ioreg command and found out that it too had an LG panel. I examined and tested it very carefully and on the first day there was no evidence of the image retention problem at all. I thought all was good but unfortunately after a week or so I began to notice image retention. As before, the more days that passed the more severe the problem became.
I took this new laptop to an Apple store and again the genius was able to immediately see the problem. I was given the choice of returning the laptop (this new one is still within the 14 day return period) or having the screen replaced. I decided to have the screen replaced hoping that the replacement screen might have better chance of being a Samsung. However, the store did not have any replacement screens in stock so they had to order one.
A couple days later (yesterday) the store called me and told me that Apple is no longer replacing displays for this problem because they all have the problem (not true) and that they would be releasing a software fix for it. I told them that that was very disappointing and that I was not going to risk the $3,000 (plus lots of tax here in California) I spent on a software fix for what is apparently a hardware problem. In my experience when a manufacturer says they are going to do that it is because they don't want to eat the cost of properly fixing the hardware and the software "fix" is an attempt to simply cover it up. Now, Apple's support is way better than anyone else but I remember when people were complaining about iPhone 3G signal issues Apple's "fix" was to update the software so that it simply showed more bars at the same signal level. Also, in my case, I actually use Windows and Linux far more than OS X so a software fix for OS X is not going to help me even if it were possible to fix this in software.
So this laptop is also going back when the return period ends tomorrow. I bought another low end model at a store last night and unfortunately it has the same LG panel. I'm twice burned with LG so I'm not going to wait until the problem shows up; it too is going back immediately. Maybe I'll try once more to buy one with a good panel but I don't know. Maybe I'll just give up.
My advice to others in this situation is that if you are given a choice between returning the laptop, exchanging or having it fixed you should return the laptop and buy a new one. That way you have a chance of getting a good panel, you reset your return period and you're not stuck with something that isn't satisfactory if Apple does not come through with a fix that really solves the problem.
Carl