I've been using them for about 5 weeks now. I smoked since I was a teenager and have never quit for more than a couple weeks. I'll put it this way, it's like any other smoking cessation device. The only thing that makes eCigs different, in my opinion, is that they're more fun than the others. The New York Times had a write-up about them a few weeks ago (http://www.nytimes.com/2011/11/08/s...html?_r=1&n=Top/News/Science/Columns/Findings). There isn't a whole lot of information about them other than the obvious. They're much better than smoking and the health risks appear to be extremely minimal, especially when compared to tobacco use. They're cheaper and since they're not FDA approved as a true smoking cessation device, the government isn't making any money off them (which is one of the issues the NYT hints at).
If you're thinking about using them, this is what I have to say - you have to tell yourself you're quitting. The first few days will be as rough as any other time you've tried to quit. You go through withdrawal. As well, vaping doesn't give you the same sensation as smoking. It'll keep you busy and it might actually curb your cravings but it's pretty clear the nicotine isn't hitting your bloodstream the same way it does when you smoke.
One of the things I did before I quit was measure my resting heart rate. Before I quit, I was scoring consistently around 70. Within a few days, it dropped to 60. As I'm typing this message, I just measured at 49. Just viewing this number on a regular basis reminds me how horrible smoking is.