Unfortunately, there's only been one (that I'm aware of, as of maybe 6 months ago) *independent* study involving the intake of nicotine via e-cigs. That study concluded that the inhalation of vaporized nicotine was a completely ineffective method of introducing nicotine to the bloodstream. As in, didn't work, not even a tiny bit.
However, e-cigs offer a combination of things that no cigarette placebo ever has: the physical substitute, the "feel" of inhalation, and the visual effect.
Regardless, e-cigs are another possible aid to quitting. As plaintbrain said, though, it's all about the decision. Either you want to quit smoking enough to actually do it, or you don't. E-cigs are a path.
If you want to quit, give them a try. Factoring in a whole bunch of stuff, they're just about exactly as expensive as a pack of real cigarettes ...without all the negative effects. Even if you're not sure you want to quit right now, spend ten bucks and buy an e-cig, just to check it out.