Guest blog by BusinessWeek Associate Editor Mara Der Hovanesian, who has closely followed the housing bubble and bust:

Some of the hardest hit neighborhoods across America are ones that never even got off the ground. Brand new subdivisions on the outskirts of sprawling cities in Florida, Arizona, California, and Nevada have been fast turning into ghost towns. Foreclosures are soaring on homes never occupied because so many were purchased by speculators hoping to flip them. While many players-—subprime lenders, Wall Street, greedy buyers--have been taken to task for contributing to this epic housing meltdown, scant attention has been paid to the role of large homebuilders who were active lenders offering some of the most toxic mortgages in these new communities.