At least one brand of electronic cigarettes - eSmoke - has had its product tested for diethylene glycol. The product was found to be free of diethylene glycol.
The Rest of the Story
This means that at least for this brand of e-cigarettes (and probably for many, many more), there are no currently documented reasons to be concerned about adverse health effects of the product.
So far, there have been only two legitimate health concerns expressed about the product:
1. It contains carcinogens.
2. It contains diethylene glycol.
The first issue - the presence of carcinogens - has already been shown to have been without merit. The levels of carcinogens present in the cartridges was extremely low. These trace levels are in fact comparable to the level of the same carcinogens present in nicotine replacement products like nicotine gum and nicotine patches. Importantly, the levels of these carcinogens is orders of magnitude lower than that of the same carcinogens in real cigarettes, providing evidence not only that there is no reason to worry about the carcinogens in e-cigarettes, but also that these products are much safer than conventional cigarettes in terms of cancer risk.
The second issue - the presence of diethylene glycol - is probably an issue only with a few select e-cigarette brands. As pharmaceutical grade propylene glycol is readily available and contains no appreciable amount of diethylene glycol, this problem is most likely not a widespread one. Today's revelation documents that at least two common e-cigarette brands have been tested and been found to be free of diethylene glycol.
Given that both of these concerns have been dismissed, at least for some e-cigarette brands, that leaves us without any documentation of a reason for concern over the relative safety of electronic cigarettes compared with conventional ones. This does not mean that further studies of potential adverse effects (i.e., clinical trials) are not necessary. But it does mean that there is no reason to spread alarm among e-cigarette users that they are endangering their health by using these products.
The rest of the story is that quite the opposite appears to be the case. By quitting smoking and switching to e-cigarettes, smokers are greatly enhancing their health and helping to stave off serious and potentially deadly health consequences.