I've only been at this for about 6 weeks, but I'm about 1 ml per day of 24 mg/ml. I had no idea I was at the low end, since I smoked a pack a day, and I definitely feel like I'm ingesting similar amounts of nicotine.
I suspect that part of the difference is that I only have one flavor, and I'm still on my first clearomizer and coil. (They told me the coil would only last two weeks, but I haven't done any maintenance. I suspect that if I switched flavors, used more than one clearomizer, changed coils, etc., I would wind up wasting quite a bit in the process. The tank is calibrated with markings up to 2.4 ml, and when I fill it once a day, it does look quite low. But sure enough, the 10 ml bottle I started 7 days ago looks like it still has about 3 ml left in it. So if I cleaned it or changed it or changed flavors, even though it looks "empty", I'm guessing I would waste about 1.4 ml.
I'm still amazed that I haven't had to do any maintenance yet. When I do, I'm guessing my consumption will go up.