I just wrote a big long post on this two days ago but I got an error when trying to post and said fuck it.
I too got one to try out. Much cheaper than lozenge or patch for people trying to quit and I do think they are better on the lungs.
However, what you are inhaling is a mixture of propylene glycol and vegetable glycerin. Propylene glycol is what is used to make fog in fog machines. They say it is safe because it is used in a bunch of food stuff and cosmetics like shampoo. I usually don't smoke food or shampoo, so I'm unconvinced of the safety of inhaling this stuff on a daily basis.
I looked at some research, and propylene glycol is metabolized into lactic acid in the human body, which may not be a good thing for a lifter or an athlete. There also haven't been any long term studies on the effects of inhaling it in pretty large amounts over a long time, so until that comes out I'm not going to smart smoking the stuff regularly.
Right now, I would agree that they are superior to cigarettes in that there is less tar in the lungs, less smoke smell over your clothes, house, etc. I also think it is a good way to quit smoking.
Do a google for 'totally wicked'. They have models where instead of buying refill cartridges, you can get bottles of the nicotine juice and fill up your own or direct drip, i.e. drop it right into the atomizer so you don't get inhale burnt sponge when your cartridge gets low.
If you are trying to quit, you can get the juice in different strengths, and just titrate down to nothing.