As subprime mortgage-backed security performance is in a seemingly unending freefall, the rating services recently adjusted their outlook for the sector. Approximately 18.0 percent of 2006 subprime mortgage-backed securities are 60+ days delinquent, nearly 2.5 times higher than the 7.3 percent rate seen at the same point in the 2005 vintage. And 2007 subprime MBS issuance is faring even worse...