One can asses the popularity of Euro by seeing the fact that it is the second largest reserve currency as well as most traded currency after the Obama's US. However, taken in to account the combined circulation of Euro, it has the highest combined value of banknotes and coins in circulation equivalent to €800billion.
Today, Euro is followed by 16 countries with only 5 having the issuing rights and have 11 currencies pegged to it.It is the official currency of European Union and used as focal point for all European institutions.
Unlike, other currencies which are controlled by Central banks of their countries, Euro is controlled by European Central bank. Thus the countries can not use monetary policy initiatives of money supply and interest rates to curtail or spur economic growth.
This combined with vast differences in the economic stature between the countries will be some of the reasons for exodus of key member states. As a result countries like Germany, France will be severely maimed by the con-tango effect of members European countries eg PIIGS (Portugal, Ireland,Italy, Greece, Spain)
Below are some graphs to explain the differences between memberEuro states
Greece
