There is a really big difference between using plastic (which has its potential problems) and using a smart-phone.. Today's smart-phones are essentially mini-computers, and have the same exact problems when it comes to viruses, hackers, and similar.
So it all depends on implementation.. But any information stored in a smart-phone, or tethered to accounts enabled by that smartphone is vulnerable for abuse. Thats the new frontier for thieves.
10 years down the line, when some of those problems might have been handled? Yes, maybe I would use it.
But now, when everyone, especially the people implementing it, are still naive about its potential for abuse? Not if my life depended on it.
Most of the people pushing this are non-technical marketeers, who has all their interest focused on the tracking and marketing aspects of it. There are enough articles written in marketing mags to show that. Having worked for and with these type outfits, my bet is that the technical guys will be overridden by the marketeers and the dollar-signs in their eyes. I know I always was, until the sky started falling. Then the marketeers started ducking and white-washing their hands. So until that conflict is resolved, I will not be using my phone for anything other than its main purpose. Talking to people.
But I am likely influenced by the fact that I am cynical technical dude who sees the holes and see people trying to break systems every day. If you know where the holes are and how to use them, you also see all the potential for abuse.
Most people are blissfully ignorant when it comes to electronic/online dangers, and they like being kept that way. It makes the world look like a nicer place to be. Until they get scammed.. Then suddenly they start screaming about why someone else did not protect them from their own actions or lack of security awareness.