This is a good time of the year to send email to your employees reminding them that if they are going to be away for the holidays they should take some steps to save energy, and money.
(free free to cut and paste from this... I stole it from somewhere else too)
Some simple steps you can take:
Power off your monitors. Many people leave their monitors on or in standby, which uses more power than actually turning them off.
Shut off or put your computer in sleep mode if you won't need your computer at all over the holidays. Note: some machines don't have an effective sleep mode so if possible, turn them off.
In general, put your machine in sleep mode when you are away from your desk, especially at night or on the weekends. Even if you're not on vacation this week, use sleep mode to help save energy and reduce emissions.
Set your screen saver to "blank" if you do need to leave your machine on so you can access it remotely. Screen savers can cause some processors to use more energy than just a blank setting, and they aren't even necessary for monitors anymore - other than providing nice eye candy for someone watching. (generating those fancy graphics requires extra CPU work and that consumes more energy)
Unplug other electronics. While you're at it, please check your area for other non-essential loads that could be unplugged or turned off over the holiday (lamps, holiday lights, electronic picture frames, etc.). This is a good idea to do all the time, not just before the holidays. Even though we employ motion detectors and timers to shut down lights, these aren't everywhere, and it saves even more if you manually turn lights and projectors off when leaving the room.
Do NOT shut off a computer that isn't yours. Ask the owner FIRST or offer to power it off for them. Some machines may be controlling critical processes that run when people aren't around or have a special shutdown procedure (not just "hit the button"). Of course, any computer in a "computer room" or "computer closet" should not be powered off except by the IT staff. You wouldn't want us to not be able to process invoices (or payroll!) because someone powered off the wrong machine.
Finally, if you're traveling away from home you might consider unplugging things at home, too - helping the environment a bit while saving your money. http://standby.lbl.gov/summary-chart.html shows typical savings for appliances. For more tips the EPA http://www.epa.gov/epahome/hi-winter.htm#effective and Sierra Club http://www.sierraclub.org/tips/holidays.aspx have suggestions.
Have a great and safe end-of-the-year whatever-holiday-you-celebrate-even-if-it-is-none time of the year!