Far from anything to do with the marketing prowess of the Twilight novels / movies and their tie-ins, "vampire power" refers to the electrical power used by electrical and electronic equipment while in "sleep" or standby mode. The "phantom load" is estimated to be around 10 percent of residential electricity use.
No wonder that there has been a call to reduce the leakage, by turning devices to OFF instead of standby when you don't need them. Chopping 10 percent off your electricity bill (and your home's carbon footprint) is nice.
In 2010, the average US home used about 11,500 kWh of electricity. A tenth of that comes to 1150 kWh per year, or about 3.15kWh per day.
Let's put that in perspective: the Nissan Leaf is rated to have electrical mileage of 340 kWh per mile (ignore the silly MPG-e number or the misleading "zero emissions": for an EV, the kWh per mile number is the only one you need).
So if you own a Leaf, you could drive nearly 10 miles each day on the electricity you save by turning your devices OFF: 3380 miles a year, which is a whopping 22.5% of the 15,000 miles the average US car covers annually. In a gasoline car doing 20 mpg, your carbon emissions savings would amount to about 1050 miles a year, about 3 miles a day.
On the other hand, if you let go of your gas guzzler and trade it in for a more gas-frugal car (and 40 mpg is no big deal any more, even in the US), it is possible to double your fuel efficiency overnight. Now we're talking a real win on those CO2 emissions: once you do that, perhaps you can be forgiven for leaving one or two things plugged in and on standby.
We have been conditioned to think "EV" and "hybrid" when the words "fuel efficiency" come up, and such vehicles come with high price tags. But it doesn't have to be that way: you can save thousands of dollars even at the purchase, by getting the right amount of power for your car; I believe that generally our cars have way more power than we really need. I'm one of those who can stand to ditch the vroom-vroom effect if that means I can save thousands. Here is my pep talk on how to buy a gas sipper for less - even without giving up on comfort or safety.
Right now, a car doing less than 30mpg is a dinosaur.