OK, so what happened in June 2011?
mtGox was hacked and some 500k BTC stolen.
don't think it will ever happen again, & if it does i doubt the price will drop like that again coz everyone will buy like mad, keeping price up
ATM current production from coinbase is about 7200 BTC so that is 6*7200 USD that needs to be pumped in daily to keep the price at current levels.
That is, we assume that all the mined coins are sold off on the exchanges etc. and not hoarded.