This solved my questionRe: iMac 27" Screen goes black repeatedly, but then settles for a while?
I picked up my iMac today from Apple. They replaced the LED backlight boards. I've been using it non-stop tonight (about 6 hours straight) and have not experienced any problems. Everything on the Mac is how it was, the drive was not erased for a Lion reinstall. So far so good. If it starts acting up, I'll post another update.
Thanks. I still havent brought mine to an Apple Store because the nearest one is in Phoenix. However, I noticed whenever I watch something on Netflix, on the iMac, the black screen problem doesn't occur. I'm not sure why, but it doesn't. After a while of not watching something, it went black again, so I start up Netflix, and it goes away. Hopefully this next week I'll be able to take it to Apple to see if they can do anything about it and tell them about your solution.