E-Cigarettes are becoming more and more popular and I’m happy to report that TSA has no problem with e-cigs being packed in your carry-on or checked bags. Now as far as using them on a flight, I would suggest you contact your airline and see what they have to say. And, while not recommended by 9 out of 10 dentists, candy cigarettes are permissible as well.
Since I’m on the topic, I’d like to touch on a couple of things. Once upon a time, cigar cutters were prohibited, but these are permissible to pack in your carry-on luggage.