There have been many stories about home buyers deciding to walk away from mortgages rather than pay them. In some cases, it's out of distress, in others, it's a purely financial decision.
This statistic blew my mind:
"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."
From Borrowers Abandon Mortgages as Prices Drop (You probably can't read it without a paid subscription. Sorry).