>>So what's going to cause a collapse? (housing)<<
I remember back in early 2000 when some asked the same of the Nas. Whta we will see in a housing is a lack of buyers. Other than lower and lower interest rates and strong demographics, the housing boom or bubble has been extended by offering mortages to those that in the past were not able to qualify. Sub-prime lending has added many new buyers. Once we work through this new crop of buyers it is hard to see where we will find others as at the same time new home buyer demographics are turning down. Of cousre and rise in mortage rates will end the boom in a heart beat.