I wrote a few weeks ago in Tech Tails #688 about a 27-inch iMac with a screen flicker issue shared by many on Apple’s discussion boards and around the Internet. Apple addressed these concerns yesterday with a firmware update as predicted here in Tech Tails.
If you have a 27-inch iMac with an ATI Radeon HD 4670 or 4850 and a screen flicker issue, select Software Update from your Apple menu and install this update!