An estimated 927 people own half of all Bitcoins

"Ownership of Bitcoin appears to be highly lopsided.
This has long been a source of consternation in the Bitcoin community, and people like the FT's Izabella Kaminska have written extensively about the implications of this apparent cartel on prices — basically, they get to dictate them, and the rest of us are just price takers.
Now Finnish entrepreneur Risto Pietilä, an active member of on Bitcointalk.org, has offered an estimate of just how severe this ownership imbalance could be.
He based his calculations on data from Bitcoinrichlist.com, which has trawled through Bitcoin's master ledger — the Blockchain — to offer a rough guide to distribution as well as activity on Bitcoin exchanges.
We ran the calculations by Martti Malmi, one of Bitcoin's earliest developers, and he agreed they were basically sound. "The order of magnitude seems right," he said in an email to BI.
So, as of Dec. 3., using a price of $1,000 (which is basically where we are now), and assuming 12 million Bitcoins in circulation, here's the breakdown: 47 individuals own 28.9% of the approximately 12 million Bitcoins in existence so far. Another 880 own 21.5%, meaning 927 people control half of the entire market cap of the digital currency. Another 10,000 individuals control about a quarter. And the rest of us (around a million of us) get the crumbs (500,000 are out of circulation, whether through government seizure or people losing their passwords)."

Source:  Business Insider, 10th December 2013