TL;DR: The number of bitcoin holders has just surpassed 2 million mark! The growth is happening in the holdings of 70 bitcoins or less, especially in micro-holdings of 1 bitcoin or less.
Great news. So Bitcoiners are now 0.03% of the world population. Imagine what could happen when 3% of the world population becomes Bitcoiners. The exchange value can increase by 10 to 100 times.
Don't get too excited. Some of the data used to support the 2 million claim has turned out to be false (Mt.Gox sources). This estimate is likely to be revised downwards, heavily!
I think the evidence points out to 700k-1M users but would like to hear comments on the methods and not just "voting on the results" 
That's actually GREAT news.
Cause if Bitcoin achieved this level of success with less than 1 million users then imagine what will happen with 10+ million.
The public ETF license, coming later this year, something I said was a done deal way last year, will easily bring in 9 additional million investors in the US alone.
The reason is that money managers, Hedge Funds, Mutual Funds, IRAs, 401Ks, etc will all start putting something in Bitcoin and one can only imagine how quickly $100 billion in new capital will add up given there's trillions in investor money floating around in all the various account types.
At this point, BTC, and select Cryptos, are quickly approaching a low risk valuation while their upward profit potential are still astounding, such potential the investment world has never seen.
100,000%+ Crypto-Coin investments will be a reality in the next 12-24 months.