I have one as well, and the original screen was an LG (purchased a week after they launched the computer, but not delivered for another month). I heard about this defect in the above-mentioned thread about two weeks after launch, but didn't notice anything for about 6 weeks after receiving it. Then the trouble started.
Exchanged for another screen - except it was another LG. Which promptly developed image retention after two weeks. This time, Apple Store 'geniuses' made out with a bullshit test that it was 'normal' and 'expected' - to which I pointed out that the Samsung equivalents had no such 'normal' ghosting at all.
Fought with the fuckers for 3 weeks. Finally, I had to threaten to return it for a full refund off my credit card when they finally gave in. I kept pointing out that a laptop costing over $3k Cdn has no business exhibiting such behaviour, and that otherwise I actually was very happy with the computer besides this one issue. They finally replaced it with a Samsung-manufactured screen - and this was back in September; totally flawless screen since the final replacement.
The clincher? You just have to ask them if they would be happy with an expensive machine that showed this shitty display themselves.
The computer itself is really a dream to use now. And yes, it's the best purchase I've ever made as well. Despite all the bullshit to get there.