Wow, that's unfortunate about the LG vs Samsung screens. How could you tell what screen you have? I'd like to spread awareness about this to my friends.
If their displays are faulty, there will be a noticeable ghosting effect when a window is left in the same place for a long time and then moved somewhere else on the screen. A faded "ghost window" will remain in its place. Another issue is stuck/bright pixels, there may be several bright white pixels that never change.
If your friends aren't seeing noticeable problems though, there's nothing to warn them about. It's not that one display is inferior to the other in terms of color accuracy or brightness or quality. One display (I think it's the LG) has a noticeable ghosting and bright pixel problem in some cases.
Use it at your own risk, but I found this test from Marco Arment to be one of the most popular ones to determine if your retinaMacBook Pro has ghosting / burn-in problem.
I am not sure which one of two manufacturers display is faulty, but per discussions on Apple's support Communities (https://discussions.apple.com/message/18669644#18669644), rMBPs carrying display panel from LG tends to suffers from this problem more commonly compared to those from Samsung.
EDIT: Just ran this test on a retinaMacBookPro to determine if I have a LG or Samsung Panel and found it to be working.
This was pretty easily fixed, though. The technician took one look at it, nodded, and I had it replaced for free while on Christmas + New Year vacation.
Maybe in the US. But in the Philippines, we're out of luck.
EDIT: I mean about the replacement part. Sure, they'll probably replace it after a several back and forth, plus the replacement will take serveral weeks.
