What would happen if the world switched to a single currency?

Question

What would happen if all countries suddenly stopped using local currencies and adopted a global currency (like the Euro, but for everyone)?

Answer 1

Countries would no longer have control over their own monetary policy. A single central bank would be able to control the interest rate of the most creditworthy country and the rates in other countries woul be higher depending upon their credit quality. The only policy remaining for countries would be fiscal policies. If borders aren't opened up to allow free flow of labor from high unemployment countries to low ones the business cycles could become more severe. Finally curreny traders like me would have to find other work