This cannot be answered definitively at this time, as there have not been studies yet to attempt the quantitation of nicotine, if any appreciable amounts are indeed present, in second hand (or exhaled) vapor.
However, the best estimates (of those experts who do not have an ax to grind against ecigs), are that any nicotine likely to be present in exhaled vapor is minuscule, and not likely to present any harm or danger to bystanders.
For example, from Dr. Michael Siegel, of the Boston University School of Public Health:
"There is no evidence that the exhaled vapor contains any significant amount of nicotine. The lungs are fantastic at extracting nicotine (this is why cigarettes are such an effective nicotine delivery
device). We know that in the exhaled smoke from smokers, the level of nicotine is extremely low. Secondhand smoke itself does not expose nonsmokers to high levels of nicotine." And,
"Even if the vapor contained nicotine, it would be highly diluted by the time it reached the nonsmoker. The vapor dissipates almost instantly, and there is no evidence that there is any meaningful exposure to nicotine among nonsmoking bystanders."
The Rest of the Story: Tobacco News Analysis and Commentary: Action on Smoking and Health Claims that "Secondhand" Electronic Cigarette Vapor Causes Heart Attacks in Bystanders
Dr. Murray Laugeson of Health New Zealand came to much the same conclusion in his October 2008 report on the safety of Ruyan ecigs. Again, based on his analysis of published data on nicotine absortion, but not actual data on
ecig vapor, he states:
"Inhaled nicotine in cigarette smoke is over 98% absorbed, and so the exhaled mist of the e-cigarette is composed of propylene glycol, and probably contains almost no nicotine;"
http://www.healthnz.co.nz/RuyanCartridgeReport30-Oct-08.pdf
And finally, Dr. Joel Nitzkin, Chair of the Tobacco Control Task Force of the American Association of Public Health Physicians, has this to say, not necessarily specifically about nicotine but about second hand vapor overall:
"Smoking bans have been universally justified on the basis of the risk posed by environmental tobacco smoke to non-smokers. Most of the air pollution due to cigarettes is due to sidestream smoke – the smoke that curls off the end of the cigarette when no one is puffing on it. E-cigarettes have no sidestream smoke. E-cigarettes also have none of the toxic products of combustion produced by conventional cigarettes. It is therefore unreasonable to ban them on the basis of risk to non-smokers."
http://www.aaphp.org/special/joelstobac/ecigcontext.pdf
