Overnight power costs: $1.72b

How much do you think it costs to power all of the computers left on overnight? According to a recent study, $1,720,000,000.00. And that's just in the USA. It's a stat raised by a company keen to sell power management software, but it is still a pretty freaky figure. 30% of corporate computers are left on overnight. Is this the fault of lazy users, or unreliable sleep / hibernate settings that make people scared of powering down?