Posted also on another Thread, as this problem is spread along the board:
I have the same experience in Spain:
I purchased the iPad Air Wifi+cellular 128 Gb on November 1. Received it by courier on Nov. 6, and right after unboxing it I noticed a dark area in the left of the display.
Looking carefully I see a dark area of about 1 cm on the left, and a brighter area (the same size, top to bottom) just near the shadow.
I drove to the nearest Apple Store on Saturday to ask for replacement and discovered the same screen problems on the other units available. We unboxed 2 new units and checked the units on display. All have the same issue in more or less the same amount.
People on the Apple Store not noticed it as it's more difficult to see with the standatd coloured background, or with web surfing. If you look at a blank page (in Safari or othe app) with a mid backlight adjustment it's here.
So I think it's a very common problem, present in a big amount of units of the first production run. Just most of people haven't seen the problem yet.
For me this is a clear lack of Quality Control. We can't accept a high quality product with this faults.
I just asked Apple for a replacement. In 3 to 5 days I expect to receive the new unit, at this point thinking it will have the same problem more or less.