Not back to vaping just yet (waiting on some kit and other things), but when I was, it was probably about 2-6 puffs every 30 mins or so, which is roughly equivilant to the amount id puff on cigerettes.
Guessing of course, but it certainly wasnt alot, in fact, carrying the thing around, versus having to light it etc, it tended to be like puff puff, stuff back in pocket.
I found with a high nic and some wtas, id be satified after fewer puffs versus analogues in a single session. But then Id have more sessions, due to not rolling, lighting, and being able to reach straight into the pocket. So id guess its about the same.