This is an article from one of my favorite writers on macro and micro-economics. He always finds really interesting viewpoints about subjects:
http://www.investorsinsight.com/otb_...?EditionID=149
Very interesting article with lots of great graphs.
For me, it's the deviation of the price of rent vs mortgages. Here in San Diego, housing is rediculously overpriced compared to rents. It makes much, much more sense to rent here (as it does in many other cities)..