Wow, it's amazing how so many people are reporting uneven tinting, let alone screen issues in general. In portrait mode, the bottom of my screen also exhibits warmer, yellowish whites compared to the bluer whites at the top of the screen. It's very subtle, but nevertheless present, and ultimately unacceptable for a product at this price point. Hard to believe that something as fundamental as display integrity is still an issue in 2013. But sadly, like someone said earlier, this is something we've kind of come to expect from Apple.
I want a good screen, I really do, and I don't think it's asking too much, but at the same time, I really don't want to have to play the Apple lottery because the next display could be worse. It's a frustrating experience buying an Apple product anymore.