Seriously though, if you can't notice it when you are working, you have no reason to return it. If you find it distracting, you have every right to return it.
I have the 23" and back lighting isn't totally even. Not as bad as yours, though when do I notice? Only when a solid black image up. When do I do that? Hardly ever.
What exactly is defective? The Bacllighting or that weird tape looking thing near the bottom middle of the screen? I have uneven backlighting on my iMac and it doesn't bother me. Don't let it bother you, just move on unless you really can't stand it.