I'm not saying it would trigger it, just that it is a symptom of a system thats gone way out of bounds. I don't even think it will be a mortgage default crisis per say (though when the values go down everyone who's currently stretched to get into their place will be screwed for a while). People parking their money on real estate could all try to get out of a given market at once, making a run on housing values. Strange thing is, thats the only case in which I am personally able to buy a house, so there's a large part of me that wishes it would happen so there would be more units on the market and affordability.