I have resided and worked in Europe, Africa, Asia and Australia and have never seen gold being used as currency together with any other.
I must tell you that if that were the case then Gresham's law would apply and the bad currency (paper money) would have expelled gold out of circulation.
http://en.wikipedia.org/wiki/Gresham%27s_law
I must also tell you that I have never seen paper money being taxed when it changes hands. Nor have I ever seen the local currency being subjected to CGT on disposal. For income tax purposes the term asset represent value of ownership that can be converted into cash. So foreign currency can be an asset but not the local currency, because is already cash.
