The Conspiracy Of The Freezing iMacs
So far the only way many users have found to resolve graphics freezing issues is to have Apple replace hardware. Lending credence to the numerous complaints strewn about various Apple-related web sites is the following:
“AppleInsider itself can attest to the symptoms, which first manifested in a review unit weeks after the August release. A sure sign that the system is near a freeze are very brief white streaks that dart across the screen -- a behavior witnessed with high-end video cards running past their limits. Visual corruption in certain programs, especially those that require a full-screen mode, also hint at an impending lockup.
The issue further appears to be disconnected from the operating system, as it also manifests in Windows while using Boot Camp (which, incidentally, incorrectly lists the video card as a Mobility Radeon HD 2600) and also appears regardless of the version of Mac OS X installed. iMac users in Apple's support forums complain that upgrading from Tiger to Leopard often exacerbates the problem, freezing when a game, screensaver, or a similarly more intensive task than the standard Leopard desktop is activated.”
Apple is notoriously slow to admit to hardware defects, and often won't take responsibility unless forced to do so by a government body. If your office is sufficiently geeky and you don't follow football, we might recommend a betting pool based on how long it will take Apple to come clean about this potential defect.