Central banks do not have self control. The US current account is being funded by Asia. In order to fund this, Asia has been funding 3 billion dollars a day to the US. The US trade deficit and US national debt is just ridicious. Check this out.
http://www.brillig.com/debt_clock/
Now, US (fed) prints money which Asia has been buying to prop up the US dollar. How does Japan and China fund the US? They print money out from nothing also. This is a big problem. Nothing is pegged to currencies. When Japan and China realize that they cannot fund US anymore, they will withdraw their money and then the US dollar will feel the pain.