Here are my feelings on your questions, hope they help.
It does seem to me that everyone seems to report mostly similar reactions to e-smoking, but with subtle invidual variations that appear to be linked to each persons own day use.
a) not feeling breathlessness
Yes I have over the last month or so noticed my breathing does seem a bit easier and my overall lung capacity seems to have improved, without comparative pre and post testing this is a subjective response. I do notice that if I e-mist (new word) for a lengthy period of time, which is easy to do as there is not and end point to using them as you get with tobacco products. I get a sort of tired feeling in my lungs, it's hard to be accurate what the feeling is, but tirednes is the closest I can come to it. I think this could be caused by the propylene glycol being matabolised into lactic acid in my lungs, lactic acid is the by-product of exercise in muscles and causes the tired heavy feeling we get after strenuous activity. This does seem to pass quite quickly though.
b) better taste
This is a bit difficult to quantify, e-mist (using a new word

) has a completely different taste/flavour to tobacco smoke, at first I wasn't sure I liked it, now I do. I have also found that smoking cigarettes is no longer pleasant, I don't like the taste of them anymore. Cigars I still enjoy as I do a pipe of cavendish
c) sleeping
Probably because I was extensively using my new toys, my nicotine levels were raised to very high levels. Nicotine is a stimulant so yes I did have some sleep disruption. prior to e-misting I'd spend 7-8 hours in bed per night, this reduced to 6.5-7.5 hours. Falling asleep aslo seemed to take a bit longer than it previously. Once I got to sleep there didn't seem to be any lack of quality. I have not noticed any increased tiredness levels during the day. I have modified my end of day use and now try not to e-mist for an hour or so before going to bed, this seems to have reduced the changes I noticed at first ... I have gone back to 7-8 hours in bed and now seem to be able to fall asleep as I used to.
d) more energy
I do definately notice an increase in the stimulant effect of the nicotine I'm inhaling, it seems to have a greater effect more rapidly than smoking cigarettes in particular. Cigars and a pipe is a different effect because for the most part the smoke is not inhaled but in general held in the mouth and then exhaled, nicotine is not as readily absorbed into the blood stream through the mouth as it is in the lungs.
For example I used to smoke three cigarettes in the morning and never really noticed the effect of the nicotine, now, with my morning e-misting I certainly do notice the nicotine hit. I think this attributable to it being just nicotine I'm inhaling and not the negative result producing by-products of tobacco smoke, particularly CO (carbon monoxide) and CO2 (carbon dioxide) plus all the other crap that is the smoke from the evil weed.
I hope that helps you.