I bought a new 15" pb from an apple store. The ones I looked at in the store had the lines. I bought one anyway, got it home, it had the lines too. It also had a dead pixel. I took it back and exchanged it, and the new one has lines as well. I know I'm going over old ground but my point is that all these pbs seem to have the same issue, and I'm very sceptical of people saying they can't see it. Either they're in denial having spent so much money, or they've got blurry vision.
My advice to anyone considering buying is that if you think this'll bother you, don't go and buy one hoping that it won't have the lines issue, because it will.
Personally, they don't bother me. The problem is barely noticeable unless you're looking out for it, and I think the screen brightness, clarity, viewing angles, brightness consistency, colour accuracy etc. is leagues ahead of what it was on the previous pbs, and this more than makes up for the lines issue. Like many others on this thread, I am a professional designer, and I'm extremely fussy about my displays. I would never trust a notebook display to proof any work that I was sending to print anyway, and I think most professionals would agree with me. You need a decent desktop LCD or CRT monitor to be sure, and lines or no lines you're going to come unstuck if you rely on a laptop screen to proof your work.