First the big caveat. The word 'unprecedented' means no one 'knows' what will happen, it is all guesses and opinion, informed and otherwise.
In a nutshell we are looking for:
Equities get sold.
If you haven't been following the Live-blog at MarketBeat, hie thee over.
MB started yesterday morning for the Jobs report and after the S&P rumors started racing up and down the street stuck with the format.
In addition they are doing individual posts such as this, bylined Mark Gongloff, at 10:35pm last night:
S&P Downgrades the U.S.: Five Things
Here he is at 1:38 this afternoon:
Downgrade Q&A: Is AA+ So Bad?