If BTC had anything actually underpinning its value we could work out the ratio of how overvalued it is. Unfortunately it doesn't - even the fact that real transactions are made with BTC doesn't change anything, as the value is so elastic that a T-shirt selling for 1 BTC 6 months ago would sell for a fraction of the BTC now.
If the currency is stable now, what exactly is making it stable? Where does the equilibrium come from? Isn't it unstable by definition anyway since it's rising uncontrollably?
Well it is incorrect to state that. Obviously, as the exchange rate increases, mining becomes more and more profitable. In fact, as of today ($50/BTC, difficulty factor around 4.9M, 25BTC/block) mining has never been so profitable in over a year(!) since January 2011 ($6/BTC, diff=1.1M, 50BTC/block)!
As volume picks up (market depth has nearly tripled in 2 months) this is a lesser problem.
I found https://bitcointalk.org/index.php?PHPSESSID=h72gmr1luhb169j1...
which shows that the top two wallets are gone now and the 80,000BTC Wallet has grown to 111111.11
The top 400 goes down to about 3,000BTC. A bunch of those could be the former largest ones broken up.
http://www.zerohedge.com/news/2013-03-10/demographics-bitcoi...
I read somewhere (source unknown, possibly unreliable) that 75% of all BTC are hoarded (ie. not in circulation).