I've just been watching some Bloomberg TV - they aren't panicking nearly as much as the other News channels are, mostly because they know a bit about economics. Again - Standard and Poor's aren't the only ratings. The US still produces 14 Trillion dollars a year, or there-abouts and that's not going to go away. Job data just came back, and your unemployment is down to 9.1% - still high, but going down.
This will not destroy the entire world - or at least it shouldn't. Investors are by nature, very jittery people, and if they get spooked they might precipitate another crisis. But that's unlikely. For the record, the massive sell off on Thursday was mostly triggered by the crisis in the EU: Italy is massively, massively debt ridden, Spain looks pretty shaky, Portugal is a mess, and Greece has so many problems that I doubt it'll remain a developed nation for much longer. Ireland isn't looking too rosy either.
But China is still making stuff. IBM and GE and Visa and Mastercard and Toyota, they're all still there. As bad as 07-08 was, we're mostly all still here, right? Some of us lost jobs, some us had cuts to our pay-checks, but most of us didn't spontaneously combust and our nations didn't go up in a wall of flames!
Bad economic times come and go. Capitalism works with cycles - cycles of boom and bust. Busts are essential to the capitalist system because the booms are always founded on too much optimism. It's always been a case in which people over-estimate the value of stuff, then there's a correction, which results in the bust, but then the next boom happens again. That's the way it's always worked, that's the way it's always gonna work. If this is your first "Big Crash" then yes, it can look pretty scary. But just look back a bit and you'll see that this sort of thing has happened many times before (except the AA+ rating, but as I remind you, S&P is only one agency).
My sympathies go out to anyone who has been genuinely affected by this crisis. A lot of good people lost a lot of money today. Many people here in Australia have lost a lot of money on their superannuation because of this (a superannuation is essentially the same thing as a 401K in the US). But it's not the end of the world, the US hasn't suddenly started to collapse in on itself and even in the WORST case scenario (people stop lending to the USA entirely), the US will still continue to function - it can just raise taxes after all.