My experience somewhat coincides with the OPs.
I've quit cigs many times for short periods of time (1-5 days) and only suffered 2 significant side effects as a result of those attempts: 1. Wanting a cig, a lot, and 2. Mild constipation. #1 was always strong enough to bring me back.
The ecig did manage to deal with the 2 side effects of quitting real cigs reasonably well, well enough that I am now smoke free for 3 weeks. However, the ecig comes with a handful of other strange symtoms that I had never felt as a result of quitting cigs in the past.
Tightness in lungs/chest feeling: Strongest in the minutes after vaping, diminishes and goes away if I don't vape for awhile. (it IS directly correlated). Physical Activity and Alcohol consumption seem to reduce the apparentness of this symptom. So far, it seems to be caused more heavily by PG than VG. This is by far the most discomforting symptom of all. When I first started vaping, this symptom was so strong that it caused mild panic. I used the ecig very lightly those first few days not smoking just as needed to kill a strong cig craving, but each time I used it, it gave me this very nasty side effect. The intensity of this side effect has subsided in intensity but has persisted with each use to present day. The presence of this side effect has led to soreness of the chest muscles at times. Another way to describe this symptom, would be like a chest that is always trying to exhale, requiring more effort to draw in a breath than there should be.
Dry Mouth/Throat: I can take in fluids all day but it is very hard to get ahead of the dry mouth issue if I am vaping. The problem is always gone after sleeping (I don't vape in my sleep), or any time I have not vaped for several hours. This symptom is directly related to vaping. Again, seems to me that PG may be the prime offender but further experimentation is necessary.
Head Aches: I don't get headaches. Or at least... very very rarely used to... Since vaping I sometimes get short lived headaches several times a day. When they do happen, they only happen in the moments after vaping.
Other thoughts:
Standard cartridge on atty designs have a propensity to burn polyfill. The results of which is the inhalation of very toxic gases. I have had a few hits like this and each time they make me feel ill for several hours. This is not healthy. I have since gone almost entirely to using cartomizers (or sometimes direct dripping)... Which also contain polyfil, but seem to wick so much better that the polyfil is less apt to ever be heated to a level of off-gassing.
The PG used in ecigs is for all intents and purposes, the same as the PG found in fog machines, which have known dangers, especially when a malfunction or custom fog machine over-heats the PG. A powerful atty running dry could probably very easily lead to the production of dangerous vaporized toxins.
The vapor from ecigs consists of high levels of PG or VG. To say that we are inhaling "water vapor" is a lie through omission. vaporized PG and VG leave an oily residue behind. In this case, that oily residue is being left in our lungs... While that residue may not contain carcinogens in high concentrations, we have to pose the question: How much different is this than leaving "tar" deposits in our lungs? Does the body have a mechanism for absorbing these oils through the lung tissue and metabolizing them safely?
With all of these considerations, I still believe that ecigs are the absolute best way to quit smoking successfully. We just have to figure out how much healthier it really is. There are a lot of unanswered questions in this new industry. The entrepreneurs who have gone into business in this industry are taking a huge risk. At any moment, this train could be brought to a screeching halt by regulation... No doubt, regulation will eventually take place, we just have to hope that it will be for the better when it does happen. If there are health risks and unknowns, I am not apposed to the product being sold, but better documentation and warnings would actually help protect those business who are selling these products.
Eric