I have a matte 24" screen, which is actually very good.
But still, the evenness of lighting is not too great.
I got an appointment at the Mac store, and got a guy who had good eyes and saw what I saw.
We discussed the matter, and came to the conclusion, that the screen was OK, and that a perfect evenness of lighting is something you will find in high-end displays.
That said, really strong differences in evenness of lighting (that you can see even on the desktop background easily) are a fault of the monitor, and you should go to get the display replaced.