I converted to e-cigs last October, at first I was using 30ml of e-liquid per month but now, 9 months later, 30ml of e-liquid will last me a year, can I go without a puff for the duration of a flight? ... Indeed I can go without a puff for a day or few.
I can understand why the airlines don't allow it ... because other smokers are struggling to last the flight without a smoke and were they to see plumes of (lookalike) smoke rising above a seat then this would set them off craving for a smoke.
However banning e-cigs is one of those rules that they cannot enforce, there is no odour and one can cup it in their hand, take a puff and swallow the (lookalike) smoke (water vapour) and nobody in the vicinity would be any the wiser.