|August 29th, 2014
Electronic cigarettes (e-cigarettes) give people the option to take nicotine in a way that feels similar to smoking, but without inhaling smoke from smoldering dried leaves. Nicotine in liquid propylene glycol and glycerine is vaproized and inhaled like you would traditional cigarette smoke. They're only a few years old so we don't have the decades of collected evidence we have with cigarettes, but from what we know about how they work they should be much safer, both for the smoker and people around them. Almost all the known health effects of tobacco come via effects of smoking plants as opposed to the nicotine consumption.
Opponents of e-cigarettes argue that "people are using them to enable smoking habits, not to quit," but this isn't a bad thing! Smoking tobacco is so deadly and so hard to quit that if someone switches to smoking vaporized nicotine that's a huge improvement. We have this idea that alternative nicotine products should be for smoking cessation only, but that's entirely unjustified. As smokers switch to e-cigarettes we expect millions fewer deaths every year, which makes e-cigarettes one of the biggest public health breakthroughs in years.
The current US legal position of e-cigarettes is a mess, and we should enact european-style regulations, making sure they list their ingredients and contain only substances generally recognized as safe. But we need to be careful not to restrict or tax them in ways that will lead to people continuing to smoke traditional cigaretts instead of switching to the far less dangerous electronic ones.
(I still don't think consuming nicotine or similar substances like alcohol or caffeine is a good idea.)
 It makes me sad to link to infoplease, but they're being very useful here. They reproduce and the data from the USDA's Tobacco Outlook Report that was discontinued after 1997, and the link on the USDA's website is now broken.