In general, we know that cigarettes are terrible for you.
There have been studies on inhalation of Propylene Glycol (http://rodutobaccotruth.blogspot.com/2011/08/e-cigarettes-no-toxic-effects-from.html) and at least in the short term, no toxic effects have been found. As far as the nicotine itself, well that’s not what causes the increased risk of cancer with cigarettes.
From these findings, we can reasonably assume that electronic cigarettes are much less harmful than regular cigarettes. There haven’t been any long term studies on e-cigarettes yet, so the long term consequences aren’t quite known yet, but again it’s likely it’s less harmful than smoking.
In general, if you’re on the fence about trying electronic cigarettes, don’t be. They’re better for you and others around you. If they don’t work out for you, the next level would be to try smokeless tobacco. Yes, I know the propaganda on smokeless tobacco would have you believe that smokeless tobacco is about as harmful as cigarettes. Truth is, smokeless is about 98% less harmful than cigarettes in every truthful scientific study done. (You can check out Dr. Rodu’s Blog and For Smokers Only to find these studies)
Anyway, smoking is one of the most harmful things you can do to yourself so any type of harm reduction measure is a good one. Just don’t take chantix/champix – those are actually highly dangerous.