Market preview: Shares are poised to follow Europe and Asia sharply lower in the brave new world of AA+, with S&P futures -2.4%. Investors stampede to safety, pushing 10-year Treasury yields below 2.5%, while gold breezes past $1,700/oz. for the first time. Italian and Spanish bond yields fall following ECB intervention. BofA -8.1% as AIG prepares to sue over toxic mortgages. Later: employment trends.