AppleInsider has reported that more than a few owners of the new shiny iMacs are experiencing freezing problems.
When the problem occurs, the system will look and behave as if it's running but is totally unresponsive to any touching of the controls, according to the report. Some suspect foul play by the new ATI Radeon HD graphics card, as most instances occur when playing games or running any video-intensive tasks.
So far Apple is aware of the problem but has yet to release a permanent fix for it. Desperate users have tried to re-install older Mac drivers with mixed results. For now, the best you can hope for is to reset the system when this occurs. If this becomes a trend, then we should all wait for a Service Pack for the upcoming Mac OS X Leopard before making the upgrade.
(Source: Crave Asia)