The market is retarded. My guess is that stocks will sell off Monday and bonds will rally. (rates will fall)
Japan has a AA+ rating. Japan also happens to be one of the US's largest creditors. Imagine that, the creditor has a lower rating then the borrower. That should say enough about these rating agencies.
S&P had Lehman bros and Merill Lynch rated AAA the day they went bankrupt. Bank of America has a 5 star rating right now.