From Kitco.com website:
http://www.kitco.com/ind/Long/april062010.html
...the US Government has been steadily reducing the maturity of its treasury portfolio to keep fiscal deficits down. Whether interest rates rise or it becomes a problem for the US Treasury to re-fund the ever expanding roll-over pools, both suggest a Maturity Wall is dead ahead. My analysis suggests it will occur no later than 2012, but it will likely be triggered earlier with the next financial default scare.
(The Maturity Wall referred to is a "tipping point" or instability crisis in the dollar. The article predicts the following going forward: bankruptcy defaults, treasury interest rate surge, then currency collapse.)