This article--thanks to Craig at UIC for the link--summarizes Larry Kotlikoff's recently published paper, "Is the United States Bankrupt?" Several places on the Web, including Drudge, repeated the scary headline.
But I think that the more interesting part of the paper is Kotlikoff's three policy proposals. One is to replace Social Security with personalized accounts, albeit accounts mandatorily invested in a global index fund. Another is to replace Medicare and Medicaid with individualized, government-funded vouchers. And the third is to replace federal income, FICA, and estate taxes with a 33% retail sales tax plus rebate.
In my opinion, they are all worth seriously investigating and debating.