the total population is around 1 or 2 % of the total population, This is a very positive opinion but I guess the number can very likely around that specially when you consider how many big markets are currently in place in china and india which have a very big portion of the world population.
We can not predict exactly how many people are using bitcoins since we are almost anonymous here and we dont know each other..
But in my speculation we are 8% of population using bitcoin in the world. .
Also The fact is that new users and even old vets have downloaded a software wallet and had the PC crash at some point and they had not backed up the keys or wallets. So we cant count exactly.