Yaron Sadan shares his fears of the US Treasury market in this article. http://www.minyanville.com/investing/articles/treasury-10-year-china-japan-middle/5/26/2010/id/28480
His arguments about the possible mechanism of failure of these markets are strong. Of course, timing is the question. No one can forecast that event with certainty.
Many state and local bond issues are in more precarious condition than US Treasuries. But all are joined together in the same orgy of debt.