Facebook group just to estimate number of Bitcoin users is not the best idea, since people won't be interested in such purely statistical thing.
The best way to monitor growth of bitcoin users imho is by observing the number of wallets instead; even tho it's not accurate, it gets you the base idea on
just how much trend bitcoin community is having.
cheers
FB may not be the best choice, but wallets are surely worse, I explained before why.
On pc I downloaded and installed at least 5 different wallets.
As webwallets, I registered in many, maybe 10 or 15, just to see the interface and services offered.
On my smartphone I tried 5 wallets.
So it's easy to see that a single user can have have so many wallets.
Number of users in this forum? Not good anyway.
Lot of people don't like forums at all, they may use Bitcoin but not register here.
Users of this forum are an underestimation of actual userbase.
On the other side, there's plenty people that just live and see Bitcoin just a good method of payment to remain anonymous.
All this mania you get to not show that you use Bitcoin... if find it ridiculous.
NSA will know you use Bitcoin the moment you open your wallet on your pc and connect to the net.
And I'm tired of this dispute about the initiative.
Who wants to join, welcome.
The others, you will be out of the group!