Did they agree to give you the samsung screen?
I never asked for a Samsung screen to be honest. Not all LG screens have the image persistence problem. If I get another LG screen I will monitor the screen and if I do get a problem I will ask them to repair it again.
I think the point here is, if you have a problem, Apple will deal with it and get it fixed. I don't think it is necessarily a problem that means that everyone should ignore the rMBP. If Apple ignored the issue and refused to fix it then that would be a problem.
Just because I have had an issue this time, would not change my decision to get a rMBP, and if given the chance again, I would still have purchased a rMBP.
You have to remember that people that people that have a problem tend to post on forums like this, the people that are fine, never say so. Forums like this tend to always give the impression that the problem is worse than it actually is.