Just some interesting math: the possible range of BTC values is between 0.00000001 to 21,000,000 (https://en.bitcoin.it/wiki/PHP_developer_intro#Precision
In theory if BTC becomes popular enough (and thus increasingly valuable, thanks to a fixed maximum) it will be traded in uBTC (0.000001), so people would treat uBTC as "dollars", and that still leaves two decimal places for cents, i.e. you'd be buying things for 123.45 uBTC. In uBTC, with the maximum value of 21,000,000BTC, there's an in-built currency limit of
By comparison, there is currently 1035.2 billion USD in circulation in the EU (http://en.wikipedia.org/wiki/Circulation_(currency
) ), which is:
So if necessary there is 20 times more uBTC than there is money currently in circulation in the EU.
EDIT - changed mBTC to uBTC