For CFOs and the people who work with them, now comes trying to deal with it all. And try to explain what it means.

"We're in unknown waters," says Anthony Carfang, partner and director with Treasury Strategies Inc., who notes that a primary impact of the change is to boost an already high level of uncertainty in the economy. "CFOs have never had to issue corporate bonds when U.S. debt itself, the benchmark, was not triple-A rated."

With the downgrade, Treasuries have gone from being viewed as riskless to carrying at least a bit of risk, adds Lance Pan, director of investment research and strategy with Capital Advisors Group in Newton, Mass. "There's no precedent," he says. "This is the benchmark from which all securities are priced."

In practical terms, of course, among corporate and other investors "Treasuries are still considered a safe haven," according to Pan, participating in a conference call. In fact, the yield on one-year Treasuries, which was at about 20 basis points in late July, dropped to 10 basis points in early August, .