Apple - If I leave my chargers plugged into the wall socket at all times, do they consume energy or present a safety risk?

It does consume energy. Feel it, it will feel warm or even hot. It doesn't use much, but it is still a good idea to not waste this. Unplug it, or buy a power strip and turn off the power strip when it isn't needed.

To find out exactly how much, you could use a Kill-a-Watt, or read the MacBook Environmental Report (PDF). The current version (MacBook, May 2010, White) says the no-load power draw is 0.010 W. The older version (MacBook, 2008, Metal body) draws 0.15 W at no load. This is quite a difference.

0.15 W means if you left it plugged in for a year you would use 1.314 Kwh. Given a price of roughly $0.20/Kwh this would cost you about 25 cents per year. If the computer is on the whole time (at 14 Kwh) the cost would be about $25/year.

I measured my MacBook Pro’s charger, and the iPhone/iPad chargers, with a Kill-a-Watt-like device, and it didn’t seem to use any significant power when plugged into the wall on its own (e.g. it was less than 1 watt).

BUT:

• I’m not sure if my device is sensitive enough to measure very small amounts of power though.

• your mileage may vary. If you’re interested in this sort of thing, I’d get a little dongle of your own and do some measuring. Mine cost about £5.

It will consume energy even when not connected to your Mac. Also, the longer you leave them plugged in, the more likely they will be damaged by an electrical surge or lightening strike etc. Best thing to do is probably have a multi-socket lead which your chargers plug into under your desk and you can just pull that out of the wall when not in use. That protects your equipment from electrical issues and saves your back from getting under the desk!