I have a C2D iMac about 3 years old, with 10.6 and all the updates. I have it set to go to sleep after 30 minutes of inactivity. Sometimes at night I will use it to listen to a podcast or watch a TV show. When I do this, it never goes to sleep. It's always still on when I wake up. The display will sleep, but not the computer. I can put the computer to sleep myself through the Apple menu, but it never sleeps due to inactivity. I'm worried that having the computer on 8 hours a night due to this problem will shorten its lifespan. Does anyone have an idea of what may be causing it? Does it have something to do with webpages being open? I always have Safari open. It's easier to leave pages open than it is to go through dialog boxes and menus to create and delete bookmarks all the time.