I've gone to AppleDiscussions only to find out that there were also many users who experienced the same thing with their 17" iMac G5 w/ iSight, 17" PowerBooks and a couple of iMac CDs. There was no solution to fix the LCD except to exercise the warranty, which in my case had unfortunately already expired. Users have even complained at the forum with the way Apple's been silent about this issue, going as far as saying that Apple's even "censored" or "downplayed" reports of these defects. I don't know much about this matter, but that's what they posted.
Affected users at the thread posted their serial numbers and traced the defective units to Apple's factory at Shanghai, China. My iMac was a week 33 (September) 2006 release with a serial number beginning with W8***** - same as affected users at the forum. They even went on to say that the problem starts with a single vertical line but will worsen with more lines in the weeks ahead.
The extended AppleCare warranty is looking pretty good on hindsight right now and I am just awaiting the cost of replacing my iMac's LCD by Ynzal. If it's more than P25T, I'm afraid I'll have to live with this vertical yellow line and just save up for the next iMac.
It seems there's no way to avoid this problem other than purchasing an AppleCare and I highly recommend everyone to get one.
Just a heads-up. Here's a screenshot:
