The only real rating that counts is the market rating, and the market--an independent, massive and most excellent rating system--is still in love with the USD. Check out the interest rate on the Treasuries.
S&P, otoh, is a political organization with an admitted agenda: to dictate US economic policy.
So, which should you trust, when they're is a conflict between their estimates?
The S&P wants to cut spending and not make the rich pay their share of taxes. That's because, duh, they're controlled by the rich. It isn't complicated. And their rating has no real effect. You can not name a major investor who gives a shit about the S&P rating.
Further, the US will never default, which is why the world still parks its money in the USD. How could it default when (I'm going to yell now because it's amazing how few people understand this) OUR DEBT IS DENOMINATED IN OUR OWN CURRENCY.
That means, to some extent, it's an illusion. We can literally print up a trillion dollar bill and give it to China anytime we want, in full satisfaction of the debt. That's why our national debt isn't related to your personal debt. It's apples and oranges.
And then there's this, for the morons sweating "who owns us." The vast majority of our debt is OWNED by us. By US. Not by any other country. So again, what sense does it make to worry about how much money we owe ourselves. What sense does it even make to think of it as a debt in the traditional, personal sense.
So calm the **** down. This downgrade is just more Tea Poseur bullshit, and worrying about it is retarded.