check out this:
Rich-Get-Richer Effect Observed in BitCoin Digital Currency Network, August 22, 2013

Econophysicists studying the way people accumulate a new form of digital currency say they have observed the famous rich-get-richer effect for the first time.


http://www.technologyreview.com/view/518541/rich-get-richer-effect-observed-in-bitcoin-digital-currency-network/

[edit]: maybe if it gets too concentrated it may implode due to a shrinking users base