LOL Jeffb, and quite true.
Newbies don't inhale as deeply, don't take as long of draws of their eCigs. Why? Because their lungs are still too full of tar buildup. They'll be lucky to go through 3ml a day for the first week or so.
The experienced vaper, one whose lungs have healed, can take those longer needed draws. Their draws now are almost equal to a real cigarette. They still, however, find it difficult to take a deep inhale like they did with their smokes, so they vape a little more often instead. The experienced Vaper will go through a good 3-6ml a day on average. This, of course, depends upon their delivery system. Sometimes 1ml of that is wasted in piddle puddles on the battery connection, etc...
With that said, the Average ex 2 pad smoker now Experienced Vaper vaping 5ml a day to achieve the same nirvana as their 2pad habit, can say that 10 ml of juice equals roughly 80 cigarettes. But then, I don't do math, so I could be oh so wrong. I know I'm wrong. You know those 5 out of 4 people who can't do math right? I'm one of the 5.