I have heard this mentioned in a rather "let's not get all panicky" sort of way. This graph from Zero Hedge shows gross domestic product of the United States, and total debt (including, I think, the off-budget Social Security debt):
There's a reason that Wyoming's lower house is proposing contingency plans for the collapse of the U.S. government, and this is one of those reasons. How long do you think the national debt can continue to grow faster than gross domestic product before everything collapses? I am not interested in living in a Mad Max world. Are you?