I experienced painful eye fatigue after upgrading to the LED-backlit MBP. I got some quite expensive eye testing done, only to find my eyes were in good shape. My understanding of the problem is that the LED dimming is done using rapid power cycles (you can't really dim a LED). Some people are highly sensitive to the cycles, I guess I am one of them.

I found that 6 squares below full brightness is OK for me, but I still get eye pain sometimes. I'm now going to try changing the color profile.