Mine worked fine for 2 years. Then for a couple/few weeks it would briefly flash black, so brief I was not sure I was even seeing it.The it got a little more frequent, and then at the end would just go to black. If I unplugged it and plugged it back in it would work for a few minutes and then flicker and go black again.
There are basically, three parts to these monitors:
661-5542 LCD Panel 27" LED Backlit $794
661-5543 Power Supply $128
661-5544 Logic Board $124
Some have had luck replacing their power supply from a 3rd party source. I did not suspect the power supply since my laptop was plugged into the monitor and it was still charging and the USB ports were still working.
I took it into the Apple Store, out of warranty, hoping for the best. I was able to get it to flicker in the store, but left before it got warm enough to black out. We surmised it was the logic board - $128 + $39 labor + tax.
They replaced the LCD Panel and the Logic Board. While quite dismayed about the situation, I feel like they took care of me.