Glad to see all the posts and that it has made people think and talk.
So the "Unsatisfied Vaper" phenomena may well be a more complex thing than we really know. Involving aspects of basic human nature, addictive tendencies, vape mail love, etc. It is in essence seeking after the unobtainable. The ultimate vape, or high, as it were.
Let me attempt to categorize this phenomena as it applies to vapers and vaping, and I am not trying to label anyone or anything, I just see difference aspects of the cigarette satisfaction equation or the lack thereof which is different for every individual:
1. There are the
flavor chasers (which another poster mentioned). No flavor is strong enough or good enough for this vaper. Some flavor chasers may find their desired flavors and their "sweet spot", but for others it may be a continual and never ending quest. I count myself as one of these vapers. I might like something, but then I try something else, and my previous favorites are no longer my favorites.
2. There are the
vapor or cloud chasers.

Here too, some are able to reach their desired satisfication level, but for others, they literally will not be satisfied until they have converted themselves into living chimneys. As Pbusardo noted jokingly, but which I believe has a basis in reality.
3. There are the
throat hit vapers. Throat hit is not a big thing for me, but for others it may be very important. Again, some will find their desired satisfaction level, others will require the equivalent of a Karate chop to the throat before they are satisfied and maybe not even then.
4.
Draw: Some like it stiff others prefer loose and airy. The reactions to the original Protank's draws are clear and ample evidence of at least some level of dissatisfaction and of peoples individual preferences. For me, I found the right draw on the Davides, but not until I had covered up two of the three airholes. And still, their is a part of me that wishes there was another airhole in the things, cuz I feel I am not totally there yet.
5.
New Vapers: Due to the steep experimentation and learning curves, it may take sometime to find their desired level of satisfaction. Many will find it, others will not. Some will give up and go back to smoking. I count myself as a new vaper, as I am less than 3 months in. So this may be a part of it for me.
6.
The Hobyist/Tinkering/Gagdet loving Vaper: The sheer variety of choices when it comes to vaping and vaping equipment is mind blowing. These vapers really enjoy the hobbyist aspects of vaping. It is very much like a kid in a candy store. And there is a desire to constantly screw something new onto their device, or delve into the world of DIY E-liquid and rebuildables. Vaping becomes for them, in many cases, more than a hobby, it becomes a lifestyle. Indeed the whole vaping thing is something of a subculture. I count myself as one of these, and herein may lie the real joy of vaping.
7.
The Fad or Trend chasing Vaper: Because of the evolving nature of electronic cigarette technology, a new device is always coming out, or another way of doing things is discovered. None of us want to miss the "vaping boat" and for some vapers the social (facebook'esque) aspects of vaping are very important. It is very much "Keeping up with the Joneses" as it were.
Many vapers can relate to some or all of these, and it is likely a complex cocktail of many things that come together. A very interesting and enjoyable topic. Thanks for all the replies.