As of July 2013, currency in circulationthat is, U.S. coins and paper currency in the hands of the publictotaled about $1.2 trillion dollars. The amount of cash in circulation has risen rapidly in recent decades and much of the increase has been caused by demand from abroad.
So we still have a long way to go to supersede fiat currency. The thing is, fiat cash is being printed like toilet paper and it decrease in value, where Bitcoin increase in value. ^smile^