A Boston University School of Public Health (BUSPH) study suggests that e-cigarettes are much safer than tobacco cigarettes.
E-cigarettes do not produce smoke and thus do not come with the thousands of chemicals found in cigarette smoke. According to the authors of the study: "Few, if any, chemicals at levels detected in electronic cigarettes raise serious health concerns. Although the existing research does not warrant a conclusion that electronic cigarettes are safe in absolute terms and further clinical studies are needed to comprehensively assess the safety of electronic cigarettes, a preponderance of the available evidence shows them to be much safer than tobacco cigarettes and comparable in toxicity to conventional nicotine replacement products."
There are also interesting findings by Expert Reviews Respiratory Medicine on The Emerging Phenomenon of Electronic Cigarettes which took a look at the potential smoking cessation capabilities of e-cigarettes and how its positive aspects clearly outweigh its negative aspects.