
Good summary of history and implications for the future (I only quote a snippet at the end):
http://www.zerohedge.com/news/2012-10-10/guggenheim-gold-and-unsustainable-return-bretton-woods
It's quite clear that reserve currency status is being challenged by China and other interests.
...
The U.S. gold coverage ratio, which measures the amount of gold on deposit at the Federal Reserve against the total money supply, is currently at an all-time low of 17%. This ratio tends to move dramatically and falls during periods of disinflation or relative price stability. The historical average for the gold coverage ratio is roughly 40%, meaning that the current price of gold would have to more than double to reach the average. The gold coverage ratio has risen above 100% twice during the twentieth century. Were this to happen today, the value of an ounce of gold would exceed $12,000.
The possibility of an upward revaluation of the official price of gold should not be minimized. Although I do not anticipate or advocate a return to the gold standard, an upward revaluation of gold by one of more central banks is possible. If the Federal Reserve, for instance, announced that it stood ready to purchase gold at $10,000 per ounce, the gold-coverage ratio of the dollar would return to 75%, roughly where it stood at the beginning of Bretton Woods. This could restore confidence in the value of the dollar if its ultimate role as a reserve currency were to be challenged.
...
http://www.zerohedge.com/news/2012-10-10/guggenheim-gold-and-unsustainable-return-bretton-woods
It's quite clear that reserve currency status is being challenged by China and other interests.