2012 could prove interesting. Social security payouts will start to exceed taxes by increasingly larger margins every year as the baby boom starts to retire. The "surplus" of the past 4 decades has been spent in general revenue so the only ways to address that problem is increase retirement age, increase SS taxes, decrease benefits, further increase the budget deficit, increases taxes, or all of the above.

The other viewpoint is that countries hold the USD because of the U.S. anti-inflationary policy not to freely print money (a new dollar spent/printed is backed by a dollar of new debt). If this belief goes away, trillions of dollars of U.S. debt instruments could be dumped. Think post WW-II Italian Lira.......