I'm a pretty heavy smoker - at least 15-20 a day, roll ups, and I've started using a recommended brand of E-cig just recently.
I'd have to say that so far, the E-cig has proved a little disappointing. I usually need to take three drags of the thing before I can get a decent load of vapour, and it just doesn't satisfy me the way a normal cigarette does. Maybe it just doesn't deliver the nicotine load I'm used to. Still, gonna persevere, because for me it works out a lot cheaper - and a hell of a lot healthier - in not having all those poisonous additives one gets with tobacco. And it has to be said, it's certainly helped with respect to the 'habit' side of smoking - where I'd smoke cigarette after cigarette as a matter of course when working (self-employed, so no-one to bother but myself with the smoke) or playing videogames. I just take habitual drags on the E-cig instead, so it's worked out quite well in that respect.