The virtual shutdown of the subprime mortgage market and a widening of spreads on jumbo mortgage loans have further reduced the demand for housing, while foreclosures are adding to the already-elevated inventory of unsold homes.

NPR: Economic Swoon to Continue, Bernanke Says

Investor demand for mortgage-backed securities--and banks' eagerness to buy loans, package and sell them to this hungry crowd--helped create the incredible run-up in the mortgage market over the last three years.

FORBES: Bush's Bad Mortgage Medicine