I don't smoke. Never have, never will.
But the little information I've got about e-cigarettes is that you extinguish them with a button and stuff them in your pocket/bag when you're done. If this is the case then there would be no fire hazard where hot ashes or cigarette butts would be tossed with paper towels in the garbage and eventually might start a fire.
So, from a fire safety aspect, IFF the information I have is correct, I would have no problem with e-cigarettes.