I'll chime in here. For the past few weeks I to have had the same concern. I have spent quite a bit of time reading every report I can find about ecig safety. Many of the reports that claim they are unsafe, deem them so because of leaky cartridges, improper labeling, and easy access to small children and things of that nature. This kind of assessment isn't really helpful. It's the same as saying a Bic lighter is a safety hazard because it can start a fire. Nothing really gets down to the nitty gritty of what we all want to know, which is "Is the vapor harmful to my lungs?"
I don't think there will be a for sure answer any time soon since every flavor (easily hundreds) has its own new chemical make up.
I am neither supporting nor opposed to ecig safety. I have been vaping for about 8 months now, and the only side effects I have noticed have been ridiculous dry mouth(worse with some juices than others). Of course I have better sense of smell, taste, and feel better, but does that mean ecigs are safe? Certainly it doesn't. People walk around with brain tumors every day that if asked would say they feel great.
I can say in the past 2 months I have had a full blood work up, lung x-ray, brain CT. throat CT, Lung CT, and sinus scope. All scans were normal, blood O2 was 98%, although lung CO2 was slightly elevated. I asked the doctor about this, and was told that the elevation was too slight for concern. Does this mean they are safe? Of course not, but I don't know anyone who has vapped for that amount of time, and had such a great amount of tests, so I thought I would share the results.
In my opinion, only time will tell about the safety of these things. Like it or not, we are the first generation of trials being conducted.