As some one who uses an eCig I wouldn't put much faith into the claims of X% less harmful because we don't know yet.
There's just too much crap going on as the scene exploded in the past 2 years I know some people that spend more time engineering their "coils" than what JPL spends on designing mars rovers and vape at with devices that look like a battery pack of a T1000 at like 150W.
No one can estimate the current effects of the oily residue in the lungs, the interactions with the flavoring, and other components, as well as the effects of in taking heated vapor, possible metal deposition and what ever wicking media is uses (silicon, cotton, other fibers).
Although it appears to be safer because you don't intake tar and the 100000's compounds in a cigarette it could end up being just as much of a health risk for a plethora of other reasons.
So it will probably take several decades until we can begin to asses the actual health impact, and considering how many variations of possible variables (liquid base, nicotine level, nicotine source, flavor base, flavor components, wattage, coil type, wick material etc.) are there it might not be a clear cut case either.
And I also hate people that "vape" in confined spaces such as trains, luckily in the UK most places put on signs that do not allow you to vape anymore, I've been seeing people do that in the movies and that's probably the most annoying thing to see as the clouds of smoke constantly catch the light from the projector.
Vaping should be treated as smoking as far as other people go if you are with some one that would not want you to smoke near them do not vape near them, having separate vaping areas might come in the future but I don't expect to see that anytime soon, sadly the place that is affected the most is the airport, especially those with the "phone booth" style smoke areas which I couldn't stand to enter even when I was smoking.