I just bought a new eMac a week ago (I've installed all the software updates), and it has trouble going to sleep. It seems like it DIDN'T have this problem when I first got it! In any case, it properly goes to sleep if I choose "Sleep" from the Apple menu, but if I simply leave the computer idle, the screen goes dark but the hard drive keeps running.
Is there something crucial in the Energy Saver preferences which is off? If so, I can't imagine what. Or this is some sort of Tiger bug?
I trashed the System/Finder preferences, just to see if that would help. It didn't.