Realcent.org

While true, this is the first time I've heard this stated plainly as related to the recent downgrade and market reaction. The core assumption behind the current system is that US debt is AAA, and always would be. When that assumption is proven incorrect, then everything else has to be questioned.

PIMCO's Mohamed El-Erian said the loss of America's triple-A rating means "things will be different" because the global financial system was "built on the assumption of AAA at its core." U.S. creditors have a right to be "nervous," he said, suggesting the downgrade will prompt sovereign wealth funds (like China's) to seek diversification away from Treasuries.

and now they've cut Fannie Mae down a notch as well..

well fannie had to be cut, as you can't be backed by someone with a lower rating than you, as that's illogical.

The issue that comes is that the dollar could be abandoned as the world's reserve currency now, in which case it'll crash.