Paul, last year I flew from LHR to Brisbane, changing flights at SIN as the LHR flight was flying on to Melbourne or Sydney. I did notice that all pax on the flight disembarked, regardless of whether or not they were re boarding the same plane an hour or so later. Someone indicated above that this is usual practice at SIN, possibly on several airlines.
PAXboy, I've mentioned the e-cig situation in other threads, and several members here have debated airline policy and the rights and wrongs of using them in flight. My understanding is that the primary reason some airlines prohibit their use is that a pax openly 'vaping' will cause non-smokers to think he/she is smoking, and cause fellow smokers to want to light up cigarettes. There may or may not be safety concerns as well, particularly with custom/modified 'inhalators'.
I placed the dismantled e-cig (a standard over-the counter) model in a see-through plastic bag along with my phone etc when passing through security. This was only questioned on my return journey through LHR, and merely 'Is that an electronic cigarette?' 'Yes' 'Ah I see, no problem'.
As for using it in flight, I was able to do so discreetly in my seat and in the lavatory. There is no exhaled vapour if inhaled a certain way. I'm not condoning or endorsing such actions, merely stating I was able to do so without inconveniencing fellow pax or crew, and to an addict like myself, this was a bloody lifesaver.