Well, i've recently purchased a 15ml bottle of fierce apple 36mg.
Initially when i got the e-... i was smoking 18mg every day. I got a strange tic in my face and noticed several effects similar to what i get on prescription stimulants (if i take too much, anyways) and quickly bumped my intake down to the 11mg/ml range. I found this was comfortable for me to smoke all day, coming from about 30 smokes a day.
After a while, i started to realize i would kind of dig a really strong nicotine hit every once in a while, and resolved to purchase a bottle of stronger juice. I've got the apple 36mg and i've been smoking it through portions of the day.
I can say that if i smoke more than one cart full of this stuff, i get serious stimulant-like effects. I smoked about 1 1/2 cart tops of the stuff and started to get shortness of breath, headache, and heart palpitations.
It's delicious and the throat hit is, imo, better than a real cig, but i can't smoke it all the time. I have an 11mg johnson creek vg sampler pack that i'm smoking as well as some cash cherry 11mg.
So anyways, i don't smoke the 36mg all the time because that would be foolish. I'm sure some people have gotten used to it but it's just too intense a nic hit for me to get used to it. Plus the 11mg i can puff on all day like i'm a vapor dragon.