Electronic Cigarettes and Air Transport Regulation

Whilst TSA allows packing of electronic cigarettes and associated liquids in carry-on bags, the regulation regarding both airport and in-flight smoking remains vague, and both airline- and country-dependent. Consider that any answer posted here will probably be outdated soon as the regulations evolve.

Smoking In-Flight

Accordig to this site the original in-flight smoke ban includes electronic cigarettes:

On Board – The U.S. Department of Transportation (USDOT) asserts that the current law includes a ban on “smoking” e-cigarettes.

“An individual may not smoke in an aircraft in scheduled passenger interstate or intrastate air transportation.” 49 USC §41706(a)(1). “Air carriers shall prohibit smoking on all scheduled passenger flights.” 14 CFR 252.3. “Air carriers shall prohibit smoking whenever the aircraft is on the ground.” 14 CFR 252.11(a).

This policy assertion is found on the USDOT’s website here as a response to the late Sen. Frank Raleigh Lautenberg’s (D-NJ) question during a Senate Committee on Commerce, Science and Transportation hearing, “Does the [USDOT] plan to explicitly ban smoking of electronic cigarettes on commercial airplanes?”

Lacking any further information, I would say that my recent experiences with European flights suggest that electronic cigarettes are forbidden in-flight. I distinctively remember the pre-flight talk explicitly mentioning this. This was on Alitalia, Air France, British Airways, KLM flights I took over the past few months.

For completeness' sake here is an incomplete list of airlines, explicitly prohibiting the use of electronic cigarettes in flight:

• Alitalia
• British Airways
• Emirates
• EasyJet
• KLM
• Ryanair
• United

Bottom line is that the regulation will evolve over time, but it is safe to assume that electronic cigarettes (and vaporisers) will have to abide by the same rules as "smokeful" cigarettes. That is, smoking is forbidden in flight, no matter the medium. Although maybe less disturbing for neighbouring passengers, electronic cigarettes may set off smoke detectors in the plane causing quite a bit of panic. See also this question for more information.

Smoking in Airports

Although, according to this site, TSA is OK with smoking electronic cigarettes in airport terminals, the final word belongs to the company handling the airport. Thus the rules vary strongly.

Seattle Tacoma Airport

Regarding Seattle airport regulation, their FAQ pages explicitly prohibits smoking inside the terminals, without making any distinction for electronic cigarettes:

Sea-Tac is a non-smoking facility. Smoking is prohibited along the full length of the upper and lower airport drives, everywhere in the airport garage, anywhere inside the terminal and in all airfield locations. 

Smoking is only allowed in two outdoor locations:

• North end of the Lower Drive (Baggage Claim level): North of door 26, across the small parking lot, adjacent to the stairs that lead to the cruise tent lot
• South end of the Lower Drive (Baggage Claim level)

Other Airports

Thanks to @Burhan-Khalid in this answer, here is a document detailing the busiest US airports, and their policy on smoking inside the terminal buildings.

To add onto what @JoErNanO and @KateGregory have said I nor anyone I know has had any issue with people using e-cigs in airport terminals. In most public places they're A-okay too. People around me never seem to have any issue either.

However, personally, I wouldn't risk using them on a plane. What with the whole puff of 'smoke' thing and whatnot.