its pretty noticeable... pretty much as soon as you turn it on and see the apple logo you can tell, at least that's what happened to me. I returned my first one due to a yellow corner and waited a month. When I got my second one as soon as I turned it on and saw the apple logo I noticed the grey was off, and then when the big "iPad" intro screen appeared I just cringed and it was extremely obvious that it was messed up. And please note that this wasn't even comparing, this was just taking it out of the box in my room.
bottom line is: if you use your iPad for, lets say 15 minutes, (by itself) and you really don't see a tint on whites, (everything just pops and looks great) then your iPad is fine. But don't bother comparing it to other monitors, its useless. each one has different tints. I had the opportunity to play around with a perfect iPad and when I used it on its own the screen looked gorgeous and whites looked perfectly white and greys looked grey. It was only when I put it next to my mpb that I would notice a different tint. but thats just how monitors are. I don't think there's 2 screens I know of with the exact same tint
