I maintain that a good portion of the real estate collapse can be pegged on rising gas prices- there is an inverse relationship between value of exurban residential land and commuting costs. For a very long time, gasoline was a negligible component of those costs and they actually declined courtesy of highway improvements, making exurban land more valuable (a sure thing!). When land appreciation disappeared as commuting costs rose, resales and refinances went off a cliff, demand dropped off further, and people began to walk away from mortgages in negative equity. If in that whole period (2001-2008) gasoline maintained at $1.20/gallon, the game may have continued a few more rounds.