I have heard conflicting advice on this. Right now, I have my screen set to go black after a while on my newer iMac 20", but I am sure this does next to nothing for conserving power or hardware. When I have let the machine sleep, I often have minor problems when it wakes up (not seeing the mouse being the most common). So do I really gain much by powering things down into sleep mode, or maybe do I pay a price by all the spinning up and down of the disks, fans, etc.? Opinions welcome!