Money is originally an IOU for gold or other goods. The papers value was connected to the value of the deposited good and the ability of the issuer to pay back the good. In more recent times though the value is connected to trust. The trust in central banks to not dilute the supply of money (increasingly less so post crisis) and the ability of nation states to carry its debt.
The graphs of US debt you posted Minos are not adjusted for inflation or gdp. This is debt level/gdp:
[Blocked Image: http://i.imgur.com/DdnfEfM.png]
If the value of the dollar and other currencies is based on the ability of the issuing country to carry its debt things look a bit better for the US. At least provided that the forecasts pan out. In the long term the US economy is still fairly competitive and the demographics are favorable relatively other developed nations. Japan on the other hand, with a debt to gdp over 200% and unfavorable demographics is looking worse.