Just examining my screen visually, the brightness is very even with barely noticeable dimming towards the edges.
However if I use my calibrator, I measure 10% dimming on the right side and there's a negative hot spot on at the middle of the left edge with 17% dimming. This is not visually noticeable though.
I suspect the uniformity is worse than other dedicated wide gamut screens.
Thanks for the feedback. That probably is about right for a consumer panel like you mentioned. It's good enough for 99% of owners. Those who need proper monitors for critical color correction will spend more to get an Eizo or NEC. I too notice some slight unevenness on mine at the R side of the screen but it's been consistent with the ones at the store so I guess they all are like that. The backlight bleed is much improved over the non-Retina 27 Apple Cinema Display I use with my 2010 Mac Pro.