For me it was pretty much a complete failure. Although it got me off of cigarettes temporarily, I was still addicted to nicotine at the end of the day. I mean, it was still an improvement, but it was in no way a solution for breaking my addiction. This was in the early days of the e-cig, so the battery would die without warning or I'd run out of juice unexpectedly, leaving me with 2 options- smoke or suffer withdrawals. Constantly having to remember to charge up or refill was the dealbreaker, and I ended up smoking again.
My wife and I both ended up quitting cold turkey and neither of us smoke to this day. I basically wanted to kill sh*t for about two weeks, then it got better quickly. Months later I got really drunk and lit up, coughed like crazy and felt sick to my stomach. That's when I knew I beat it for good.