For me it's the money I save vs smoking. And even buying the best mod you can find is only about $150 with batteries it still isnt breaking the bank. Wohoo. I have posted in a couple of other forums all about vaping and the biggest thing other people like about the e cig being able to save gobs of money.
I can say I'm very happy with the many aspects of pv use as compared to smoking cigarettes but saving money definitely isn't one of them. I'm not saving money. Bear in mind though that I was making my own cigarettes at a cost of about $20 a week for a 30+/- cig a day habit.
I went from 510's to an eGo and stopped there as far as basic equipment. But I did invest in spares of everything for both pv's. My day to day expenses now are juice and cartos.
I'm happiest with a non-stinking house, car, clothes, whiter teeth, feeling healthier, not being a social leper, healthier cats, not cleaning windows and other surfaces as often, and on and on and on.
So does the lack of saving money bother me? No. But I do think that aspect of pv use is overrated as I don't think most pv users are saving that much if any money at all unless they are light users and cigarettes cost more than they do in my tobacco producing state. And I know they do cost more in other areas.
Still and all - dropping cigarettes and picking up a pv was one of if not the best things I ever did.