I do not trust the FDA at all. However, the problem is that a lot of people do, and until e-cigs become FDA sanctioned, our PV's will always be a fringe, specialty market. And to make matters worse, e-cigs will not have the blessing of the FDA to go mainstream until Big Tobacco and Big Pharma are getting a cut of the profits.
Now, about your original question:
Yes, we are all lab rats in this great experiment we call
vaping, be it you want to or not. Simply by being a vaper, one day you will become part of the statistics.
How do we know it's safe? Very simple. We don't.
We know it is by far safer than smoking, and there is medical data and anecdotal evidence to suggest they are mostly innocuous in the short term, with some people experiencing allergy related issues to either PG, VG or both.
We also know that the levels of nitrosamines (A.K.A. carcinogens) found in the
juice are around the same or slightly higher than the nicotine patch and gum, well below actually harmful levels.
Another thing we know is that PG inhalation has been extensively studied since the 1940's and most negative findings have involved minor to negligible symptoms, but no data actually exists (to my knowledge) on the long term (2+ years) of exposure either on humans or in the levels vapers inhale.
Now, what we do not know so much about thus far is what harmful particles, if any, may be created by the nebulization process that happens inside the atomizer, specially when it is gunked up. That burnt taste a lot of people mention across the forum is not from the filler material in the carts. It comes from the build up of old caramelized
juice at the atomizer's coil (the gunk) or the wick the coil is wrapped around burning/melting. The cart's filler is there to make contact with the atomizer's bridge, which is what wicks the juice to the atomizer's coil, so it should not not burn because it is never in contact with the coil. The exception to this of course, are cartomizers, where the filler and coil do touch.
The other very important thing we do not know yet are the effects of inhaling the flavoring in the juices. And on a side note, I think it is a good thing when the thing you should be the most concerned about when it comes to e-juice is the safety of the chemicals used for flavor.
And of course, there's the grand mystery of long term effects or lack thereof. And this is something we will never know until a good deal of years have passed and a lot of data has been collected.
Before anyone comes with the blanket statement 'nothing is really safe', let me just say that yes, even blinking when a fly is passing by can kill you. But there is a huge difference between reasonably innocuous and certainly harmful - regardless of the degree of harm.
In that sense, I personally consider PV's to be mostly harmless. Specially when compared to analogs. But the bottom line is we do not know if they are 'safe', and we probably will not for many, many years.
My advice for now? Vape on and take solace in the fact there are literally hundreds of pages worth of empirical data suggesting PV's are mostly safe and users have managed to turn back the effects of smoking without giving up nicotine or the habit itself.