Most airlines do ban the use of PVs. Their rationale is that they don't want to have to explain to other passengers that you are not smoking. However, I do it stealth style every time I fly. I really don't think they care as long as you're discrete about it. Monday I flew to Las Vegas with a pilot for the airline deadheading sitting next to me. When he sat down, I pointed at the ego in my pocket and said, "You can't sit there, I won't be able to sneak hits off this." He took a second to recognize what it was and said, "No problem, I'll be sleeping the whole time." He was right, it wasn't a problem.
So far, I've openly vaped in airports with no problems.