Yeah it's really only too much if you get nauseous, stomach pain, hyperactive, pounding heart, or maybe headaches, or maybe all the above. You don't get nearly as much nicotine absorption from vapor as you got from smoke, and different devices are more or less efficient in delivering it.
My cigarettes were .5mg nicotine, but I found 18mg too high, made me nauseous; when I tried 12mg, it was ok for a while, but after a couple hours it also made me nauseous. Once I went all the way down to 6mg, I was able to vape as much as I liked -- but, I was still smoking then. When I finally quit, I found I needed a bit more, so i went up to 8mg, but found I was still chain vaping like a mad fog machine, so I went up to 9mg. That was ok, but when I came back to vaping after my illness and month-long dual-use (smoking and vaping), I went ahead and went to 10mg, so I wasn't vaping quite so often. It seems to be working pretty well; I can chain vape with that level if I feel the need, but if I'm busy doing something, I don't get frantic about putting the mod down for a while.
Andria