According to a spokesperson, that cost-per-mile figure assumes you can travel 100 miles on a full charge -- which is not always the case. It's also not clear whether it accounts for the eventual deterioration of the battery's ability to hold a full charge. A recent test by Consumer Reports estimated the actual electricity costs to be 3.7 cents per mile, which would push the total charging costs to $3,700.

There is one final factor that we could not include in the calculation, and that's the cost of maintenance. Electric cars have considerably fewer moving parts than gas-powered vehicles, and therefore fewer things that needs fixing and replacing. There's no need for oil changes, no need to replace spark plugs, no need to service the muffler. While Nissan declined to provide specific estimates on maintenance savings, another company does: Ford, gearing up to release an all-electric version of its Focus, estimates that it will cost $1,200 less in lifetime maintenance costs than the gas-powered Focus over the course of 10 years and 150,000 miles.

Of course, the Leaf has been on the road for only a few months, so it's impossible at this point to say what sort of battery deterioration and maintenance costs that its owners will see over several years of use. Still, this preliminary calculation suggests that Nissan has succeeded in delivering a cost-effective electric car.

Performance questions

Money may be the biggest concern of the average American consumer, but it's not the be-all and end-all of the decision on which car to buy. Performance matters, too, and in this respect there are important questions about the viability of electric cars. The biggest concern is range.

"A 100-mile range is not optimum," says John O'Dell of Edmunds Green Car Advisor. "Most people in the industry think 300 (miles) would be."

But we're not there yet, and even Nissan's official 100-mile estimate is generous. Indeed, the company's website acknowledges that the range will vary wildly depending on weather and driving conditions. When driving on the highway in the summer, for instance, you'll get only about 70 miles on a full charge due to the drain on the battery from the car's air conditioning.

Winter driving taxes the battery even more. Whereas a gas car uses excess heat from the engine to heat the interior, electric cars rely on battery power for heat. When Consumer Reports tested the Leaf in cold weather, it averaged just 65 miles on a full charge.

If you live in an area where public charging stations are prevalent, that's not so much of a problem, as long as you don't mind having to stop every hour or so to recharge. But right now, charging stations are as rare as electric cars themselves, so unless public charging stations have reached sufficient penetration in your area, you face the prospect of running out of juice and having to call a tow truck. With an effective range of just 65 miles in the winter, that means you can't drive much more than 30 miles from your home before you have to turn back.

"If I have a gas car and I want to go somewhere, I know there will be gasoline on the way," says O'Dell, who is waiting for his pre-ordered Leaf to arrive. "I need a national infrastructure of charging stations to make it more than a second car."

That infrastructure is starting to grow, but as of now "it's in its infancy," says Ron Cogan, editor and publisher of the Green Car Journal and GreenCar.com. The result, he says, is that electric cars make sense for only a particular subset of Americans -- for instance, those who commute relatively short distances and people who live in areas with good charger penetration. He also predicts that most families will want an electric only as a second car.

"An electric car is a great addition to the garage, but you wouldn't want it to be your only car," says Cogan. "We all want a car that can go as far as we want, and that desire isn't going to go away any time soon."

The outlook

The early demand for electric vehicles has certainly been encouraging, with Nissan barely able to keep up with demand for the Leaf. But most experts agree that we're not at the point where the average American is going to be purchasing a Leaf or a Volt as a primary vehicle.

"Early adopters tend to buy them for reasons other than economic ones -- because they're environmentally friendly, or for the fashionable aspects of owning new technology," says Jesse Toprak, a vice president of TrueCar.com. "Those consumers are enough to purchase the first several thousand . . . but they aren't mass consumers."

Getting "mass consumers" to buy in will depend on the growth of a national charging infrastructure, as well as improvements in battery technology to give the cars a more reasonable range. And it also will have to continue to make sense economically -- which will stop being the case if the federal tax incentives disappear.

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Like all things in Washington, the future of the tax incentives is a matter of considerable uncertainty. Toprak is "assuming those incentives will be renewed," while Cogan is skeptical that such pricey incentives to encourage electric car ownership will continue, given mounting concern over the federal budget deficit.

Incentives or not, it's going to take some time for electric cars to achieve any significant market share. Cogan notes that it took a decade for hybrids to get up to their current 2.5% market penetration. So while he's optimistic about the long-term prospects for electric cars in the United States, he's not as gung-ho as Obama was in the State of the Union address.

"That's ludicrous -- it's not achievable," Cogan says of the president's goal of 1 million electric cars by 2015. "Overly optimistic would be understating the case."

This article was reported by Matt Brownell for MainStreet.