As you already told, one person can have several accounts, but I believe it is safe to assume at least 3-5 million users tried Bitcoin for short amount of time. Coinbase has at least million accounts as well, and these are verified by government isued ID - so pretty much these numbers represents real people.
thats quite interesting to know, I never thought of coinbase or anything like that. If we are only at 3-5 million (higher than i thought which is good) then you could truly class anyone whos buying into bitcoin now as early adopters. All we need to do is spread the word and get properly mainstream, And hopefully with the rising price due to the halfning we get more tv spots on the news etc to push us that bit further forward. 2016 and 2017 might be more interesting than you'd think.