So in the hopelessly optimistic best case scenario, each American household would have to pay $13,364 per year for 50 years. That is, of course, assuming that the federal government closes the deficit (fat chance), and each household does not incur additional debt (doubtful). And recall: it does not include state and local debt. According to U.S. Census Bureau data, the 2007 median household income was $50,233 -- before taxes. So you can kind of imagine how impossible even the best case scenario of $13,364 per household, per year would be anyway.
I admit this is a gross oversimplification. It does not consider inflation, which is sure to happen, and which will help a bit. But if you assume the above interest rates are real interest rates (nominal interest rate minus inflation), then this might make the 0% scenario a little more likely -- but probably not for 30 or 50 years, I hope. My scenarios also do not consider U.S. population growth, which there undoubtedly will be.
Despite its simplicity, I think this analysis shows just how dire a situation the nation's debt poses. I know there's a popular argument that we've always been in debt, so it's nothing to worry about. As these numbers continue to grow, however, I think the plausibility of that argument wanes.