MisterMe said:
You could not be more wrong. When you power up your computer, it draws a lot more power than it does during normal operation. It is generally true that electric motors draw more current during startup than they do while running at full speed under no load. (Ever notice that large electric motors dim the lights during start-up, but not a full speed?)....
Think about this a moment. Lets take the case of a PowerMac left on for 24 hours vs. one used for 4 hours then switched off. For EnergyStar certification, a computer has to draw 30 Watts or less while in sleep, or 60W for a computer and display together.
Let's say 30W for the pair. So the machine consumes 600 Watt-hours of electricity while sleeping 20 hours a day. How long does it take to boot up -- 60 seconds or so of high speed drive activity until it reaches a steady state? To equal the amount of power wasted in sleep, the machine would have to draw 36,000 Watts during that one minute, a draw of 327 Amps at US 110V. This is approximately the amount of power consumption as three heavy duty arc welders at full power for one minute. Suffice to say that if your contention was true, the Mac would be a puddle of slag on the floor.
The maximum draw of a PowerMac G5 is 6.5 amps, or 710 Watts. Normal operating draw is something like 180 - 250W
So: saying that the extra power drawn in starting up a Mac negates the savings of turning it off does not hold true, except possibly in the extreme example of turning it on and off 100 or more times per day. Yes, startup takes more power than normal running. But only a factor of 2 - 4 times, and only for a short period. The statement that startup consumption outweighs the sleep consumption is off by several orders of magnitude.
Apple's advice is if it's 8 hours or more between uses, turn it off
http://docs.info.apple.com/article.html?artnum=4701
And if you live in areas of bad power, turn it off more often.
Let's look at one more thing: letting a computer sleep 20 hr. per day for a year instead of turning off uses over 200 KWh of electricity. In terms of carbon dioxide emission, that creates, depending on how you get your electicity generated: 4000 Lbs of CO2 (coal) 3400 Lbs of CO2 (oil) or 2000 Lbs of CO2 (natural gas).