Just from last week:
Southwest passenger's e-cigarette use caused emergency landing
Airplane from Ft. Lauderdale makes emergency landing at BWI after fire detector went off.
Dec 11, 2014 LINTHICUM, Md.
Southwest Airlines released a statement Wednesday that indicated Flight 3654 made the emergency landing because a customer used an e-cigarette in one of the airplane's bathrooms, and the vapor set off the fire detector.
The pilot declared an emergency out of an abundance of caution and landed the plane safely at BWI, which was its original destination, according to Southwest.
Southwest: Passenger's e-cigarette use caused emergency landing | Maryland News - WBAL Home
US Department of Transportation consider their use on scheduled commercial flights to be illegal.
A few European airlines, most notably Ryanair, allow the use of
smokeless cigarettes (
not electronic cigarettes). See:
Similar Smokeless Cigarettes (sold onboard some flights).