Thought I'd share my experiences with the iPad Air screen issue:
Bought one just before Christmas and immediately noticed the 'bookspine' effect. Thought I would try and live with it and managed to do so for about one month before I decided to take it into my closest Apple store, as it was not acceptable that a shoddy screen should be part of a device that costs so much.
Had to book a "genius" appointment and come back a few days later. So I did that.
"Genius" fellow was struggling to see what I could see, but agreed to let me exchange it, but only once (probably because he didn't think there was anything wrong with the screen). I agreed to that, even though I didn't agree with the 'once only' exchange offer. Anyway, they ordered a new unit and told me to come back when it was ready for pick up.
About a week later I got the call to pick up my replacement.
Went in to the Apple store, showed another Apple chap my defective iPad screen issue (which this guy immediately saw and agreed with exchanging it, which was nice). He brought out the replacement unit, unboxed it, turned it on, and what do you know? It had a very distinct shadowing down the lefthand side! The light uniformity was better than my original unit, but still not good enough. Told the Apple chap I wasn't happy with the replacement screen, and since we could both compare and clearly see the difference between that screen and a demo unit with a decent screen, I was able to get a another replacement for the replacement. I then had to arrange another genius bar appointment to get them to look at my defective iPad again just so they could order another replacement. Apple chap said he would add notes about my issues so the next appointment would be a formality. Sighed and booked the appointment.
Took my iPad in on the arranged day. Had to 'prove' to them the screen was defective, as the notes added about my prior experiences were not recorded (or acknowledged). They offered to replace it (again). Fine.
Another week later they had my replacement-replacement. I held my breath and looked at the screen and it was not perfect, but leagues better than my original iPad Air. Basically said 'Yep, this one's good enough', and have a satisfactory unit now.
The only imperfection I would say about the iPad Air screen I have now is slight display uniformity issues when I tilt the screen (not just viewing angle anomalies, but I can live with it because I don't generally tilt the screen to read/ watch stuff), and I don't think the black levels are deep enough (maybe I'm used to OLED screens though).