Borrowers Abandon Mortgages As Prices Drop

Goldman Sachs economists estimate that as much as $3 trillion in mortgages could be underwater by the end of the year, leaving 30% of the country's outstanding mortgages in negative equity. Since there is roughly $1 trillion in subprime mortgages outstanding, that means a large amount of better-quality mortgages, such as prime and Alt-A -- a category between prime and subprime -- will be attached to negative equity.

"The focus has been on the [interest rate] resets," said Goldman Sachs economist Andrew Tilton. "But if you're in a deep enough negative-equity position, defaulting has its own kind of logic."