IR can be an issue, but as long as you are under warranty and your IR is noticeably bad you should get a new screen without a problem.
Just to relay my experience with this, I bought my 15" rMBP in December 2012 and it came with an LG screen, first version. I used it for six months without the slightest hint of IR. I thought all this talk of IR was a bit overblown. Unfortunately, last month I first noticed faint IR on my screen when I minimized Chrome and saw an outline of the window. It would fade after a few minutes, so I didn't think much of it and it didn't impede my usage.
It started to get a bit worse over a two week period, so I took it in to the Apple store and they ran their IR test. It passed and they sent me on my way, but told me if it got worse to come back and they would re-run the test. I was fine with this because the IR still wasn't bad enough to notice too much in regular usage.
However, unfortunately over the ensuing weeks it got a lot worse; so bad that I could clearly read text and see entire windows and applications on regular desktop backgrounds and over other windows and applications after only a minute or so on the screen. I took it back to the Apple store, they re-ran the test, and it clearly failed. They offered me a free screen replacement, which of course I took.
My repair was sent out to a service center on a Friday and I got an email on the following Monday morning that it was ready. Picked it up and the screen was installed perfectly and not a hint of IR. Checked the screen out of curiosity and it is a Samsung. A bit warmer than the LG, but an equally impressive screen.
Anyway, I would say that if you have bad IR and are still under warranty Apple will replace it. In my experience it did get worse over time. So if it is bad enough to bother you, take it in. No need to live with it and constantly worry about it becoming a long-term issue.