I did about a month of full time research on electronic cigs and the results suggest that for those trying to quit smoking but have not had success so far, it was eased considerably by transitioning to e-cigs first before trying to quit completely.

Analysis of tobacco smoke and the anecdotes from those who have transitioned points to that there are substances in tobacco smoke that can cause strong withdrawal symptoms when you move from tobacco to pure nicotine. (To lessen the non-nic withdrawal symptoms some have tried lessening the real tobacco use over several weeks rather than immediate and complete switch but I didn't find enough data points to say how much this helps)

In many cases (youth in schools) also the pressure to smoke is more about being in some group where someone is setting a bad example. I think in that scenario it would be preferable to use plain e-cig with just the vapour producing substance (VG), though personally when I was in that situation I just hated the real tobacco smoke so much that I chose to spend time in the library where as everyone else were hanging with the smokers. (thus my Agenda is to atleast convert smokers to the non-smelly e-cig if I can't make them stop entirely)

Of course, there are also some people smoking due to liking the effects of the nicotine minus the addiction. I think e-cig is quite obviously better solution and there is no doubt if I had to stand near someone puffing VG+nicotine I'd any day pick that over the hundreds of substances in "analog" tobacco smoke.

edit:

As somewhat interesting side note, during the research I acquired some most typical substances used in e-cigs and found that the ones that are used to make e-cig "taste" like real tobacco also smell horrible and the smell sticks to even hard surfaces. If anyone tried these e-cigs I would caution against any additives unless you take the time to research them - the flavours typically come in a carrier/base fluid and the retail shops do not mention what that is and some of the substances used in the flavours could be just as bad or worse than smoking regular tobacco. << That's why I haven't pushed these e-cigs on any smokers beyond seeing if they'd be interested enough to research them thoroughly on their own - while plain VG+nic is probably relatively safe compared to regular tobacco smoke, there's a high temptation for e-cig smokers to experiment with additives and then there's risk of going from "known to unknown risk".