We may not have the AAA rating that agencies like S&P gave to subprime mortgage backed securities and CDOs, but it is not the end of the world. Not that I'm a financial expert.
FWIW, that is all I can think of in this rating downgrade. The same rating agencies that are so corrupt and bought off that they rated shaky financial products that collapsed the global economy as AAA is now downgrading US debt because we didn't cut $4 trillion off the debt. Without the actions of groups like S&P, there wouldn't have been an economic collapse in the first place. Had they given honest ratings to subprime backed securities then this never woould've happened, and the deficit would be 1/4 the size it is now. Absurd.
http://en.wikipedia.org/wiki/Credit_rating_agencies_and_the_subprime_crisisThe Financial Crisis Inquiry Commission reported in January 2011 that: "The three credit rating agencies were key enablers of the financial meltdown. The mortgage-related securities at the heart of the crisis could not have been marketed and sold without their seal of approval. Investors relied on them, often blindly. In some cases, they were obligated to use them, or regulatory capital standards were hinged on them. This crisis could not have happened without the rating agencies. Their ratings helped the market soar and their downgrades through 2007 and 2008 wreaked havoc across markets and firms."