Here’s a more recent post – the US Debt is now likely to exceed GDP by 2010, next year!
The United States federal debt stands at 10.7 trillion today, or 75% of US GDP. The CBO projects that the US debt will reach 14.6 trillion by 2015, without accounting for the effects of the stimulus package and ongoing bank rescues. These efforts could easily add 1-2 trillion to the total debt, sending the debt over 16 trillion by 2015.
GDP growth may be negative for 2009, and will probably average 2% through 2015 according to CBO projections. Real GDP at the end of 2008 was 14.2 trillion, and is project to rise to 15.8 trillion by 2015, less than the federal debt at that time! Rising inflation may prevent this from happening, but will bring its own set of problems.
Where does a debt load of 100% of GDP put the United States relative to other nations? That would put the US among the top 10 most indebted nations in the world, with peers like Zimbabwe and Italy.
Source Links:
Current US GDP at Bureau of Economic Analysis
US Total Debt at treasurydirect.gov
CBO Budget and Deficit Projections – Click Budget Projections. This xls also includes economic growth estimates.
True Cost - Analyzing our economy, government policy, and society through the lens of cost-benefit 
According to IMF numbers the US debt is already at 85% of GDP. China’s is 20%. The US is already among the most indebted of the industrialized countries. I explain the politics of it more at: http://localandglobal.wordpress.com/2010/02/08/will-the-world-buy-americas-debt/