One problem I see is, we are NEVER going to be measuring apples with apples. With regards to long terms of e-smoking - 99.99% of us will have been smokers of varying degrees, habits and even living standards (city poloution V countryside chemicals). So how will anyone ever truly know what is an effect of e-cigs, and what is a cumilation of what damage may have already been done, or an alchemy of catalysts from other outside influences?
Also Everyone here smokes or smoked in diferent ways, and as such they will vape diferently too. Some draw on them like they were trying to inhale all the air from a truck tyre in one go, while others puff away quietly as though they had an everlasting pipe (Guilty as charged m'lord) and like smoking, some of us will have diferent levels of resistance or immunity to what we inhale.
So the only way we will know for sure, is if a whole new army of vapers take it up, having never smoked (and no anti is going to be happy about that) and even then, we are all still taking in so many chemicals every day anyway - how can you be sure, unless you lock them in a controlled bubble.
As for whether it will ever take off? I think TB is about right when he says probably around the same level as cigar/pipe smokers. The whole thing is too much hassle for most, especially with leaking carts, short lived batteries, the overgenerous estimates by suplliers on things like cart life etc., etc.,.
One thing that might change that (given things not becoming illegal, and more reliable products coming out) might be a true classic/cult status movie with the stars vaping away in the most memorable scenes. Like it or not, these have been a major influence in our past. (distant and not so distant).
just my 2p