I think the movement in US stock prices on Monday was mainly another indication that day-to-day prices have almost nothing to do with fundamentals of the stock or the company in question. It's all about trying to be ahead of everyone else in a trade, not investing for the long(ish) term.
I also thought it was very strange that the news stories were pointing to the stock market when it should have been the bond market reacting if there was anything new and important in the S&P report. There wasn't, of course.
Cheers,
Scott.