I quit by accident, and I think it worked out great for me. I really didn't think ecigs would work, so there was absolutely no pressure that I put on myself. Having a cigarette wasn't taboo. I could have one if I wanted. I planned on having one when I wanted, I just ended up not wanting. I can see how it would potentially help some of us who have tried to quit so many times and failed. That pressure, but impending sense of failure, yet again, can be very harsh and demotivating.
Kind of like, when you are trying to lose weight and tell yourself you are only going to eat healthy paleo vegetarian organic no carbs. The more you forbid yourself something, the more desirable it is. Then, when you do slip up and taste the forbidden fruit, you think, "Well, failed that again, might as well throw in the towel."