ZD Net’s Brian Cooley gives his insight on this age old question. He writes My position in the debate: I say, forget the thing even has a power switch. Leave it on. That way your machine is instantly available, just like every other tech product you own. It also lets backup programs, antivirus apps, and spyware cleaners do their thing thoroughly every night without slowing you down–or vice versa. That’s how the pros run machines after all.
The cost? The average PC draws something like 60 watts in normal operation. At the average national rate of 10 cents per kilowatt-hour, that’s $6 a month running all the time. Add in a monitor, and you might round up to $10, much less for an LCD. So we’re talking maybe $120 per year. (full story)