I just went to Las Vegas last week, and so did my Joye510 x 2, PCC, and 2 bottles of Liberty Liquid, 15mL.
Not problems with security at either airport on the way there or on the way back.
One of the 510's was in my pocket and used throughout the airports and during the flights. Stealthy though.
I was taking small drags and exhaling slowly so no visible vapor or very little. Mostly I'd walk to the restroom...puff away, then head back to my seat. After 4 cocktail on the flight I felt a bit ballsy...and the person sitting next to me was a smoker..so I used it in my seat. (Careful to watch for the attendent!!!) As there is no 'cigarette' smell.. I got away with it.
I dare say if I was sitting next to a non-smoker I wouldn't have been so apt to try it at my seat.
I do not recommend this.. but i think a puff or 2 in the restroom shouldn't get you in any serious trouble.
-E