A point to keep in mind: they are not regulated by the FDA (which is collecting Adverse Events Reports), and there is no way to know what chemicals are in them, and what those chemicals might do to the human body. E-cigarettes are a new phenomenon, and long-term health effects are not known, so using e-cigarettes is like participating in an experiment.
One thing is for sure, the use of electronic cigarettes is growing rapidly. As regulators catch up with the technology, and time passes, we will learn more about the dangers and benefits of vaping.