Freezing iMac Issue Due to Hardware?
Appleinsider suggests that the freezing iMac problem may be related to overheating hardware rather than any particular software issue.
They cite one user who had their video chipset replaced on their iMac who found that the problems had disappeared.
This and other reports provide increasing support for beliefs that the lockups and related symptoms are caused by excessive heat inside the all-in-one chassis.
While this remains speculative, it could mean that no software solution will be able to repair the issue. A similar but less publicized issue has affected early owners of the ATI Radeon X1900 video card for the Mac Pro. Some have noted these issues have become more prominent under Mac OS X 10.5 (Leopard) due to its increased dependance on the GPU.