I received my new iMac on May 20. It is a 3.06 with an ATI card. I have not had much time to use it until this evening. I had been been setting up some bookmarks in Safari and then was working on a spreadsheet for about an hour when it suddenly shut down. The power strip in which it was plugged in still had it's light on. The iMac is the only item plugged into the strip. I then felt around the screen, the bottom section was cool but the top was rather warm. The temperature in the air conditioned house is 71°F. Programs open at the time were Safari - which was on an idle screen as I had logged out of a site. Two sessions of Finder Entourage Excel - which I was actively using. Is this an over temp shutdown? I recall some people posting the temperature of their Macs. Are there any monitors on the iMac to see how hot it is running? There were no warnings that it was going to shut down.