The vapor from ecigs reminds me of the "liquid smoke" used in old model trains to simulate smoke coming from the stack. I'm concerned about the effects of breathing that stuff in all the time. It's not water vapor as far as I'm aware.
In the short term it appears fairly hard to get killed by glycerin. Long term it doesn't sound very good at all. In that way, it reminds me of benzene or PCBs where in the short term theres zero risk if you can avoid drowning, but the long term effects are pretty awful.
Its definitely not as safe as water. Of course the "real" problem is likely whatever else is in the fluid. Who knows whats in there.
Second-hand smoke is generally accepted as a bad thing, as is wood smoke, unsurprisingly. I've seen suggestions that wood smoke may be even worse simply on the merit that a great volume of nasty compounds are released, and the particulate material is substantially smaller (due to the higher combustion temperatures) and can enter more deeply into the lungs[3]. If it's a choice between cigarettes and someone sucking down glycerin vapors, I think I'd be much happier to accept the latter.
[1] http://www.sciencelab.com/msds.php?msdsId=9927350
Plus I hear it has dihydrogen monoxide in it which can kill you in numerous ways.