Exactly the same problem
Sadly, I have exactly the same problem on my MBA 11inch 2011 version with samsung display and samsung SSD.
Actually the one I am using right now is what I got for replacement of a previous one which had key board issue....
My point is: it's really annoying and it seems to be more common and obvious on 11 inch MBA than 13 inch. I came to Apple Store and saw gradient on other 11 inch MBAs. I am not sure if there is a difference on severity of this problem, but when I view safari in full screen mode, and some text is on the bottom of the screen, the dark bottom is quite obvious and annoying..........
I am a student and I paid nearly 1200$ for my MBA11, the quality of the display really disappoints me....
On the other hand, I will do much coding work in daily use. Also I will need to take it with me all the time. So I care much about its performance and rigidness. From my current experience, it's perfect on those aspects.
All in all, it's a ultraportable workstation, just use it and take as much as you can from it. Performance is good, display sucks. It's an "OK" investment.