From Forbes:

Yes, But Bet The House

By a margin of almost 2-to-1, economists surveyed by WSJ.com last month judged that the worst of the residential real estate slump was history. House prices will soften in 2007, the sages predicted, but by only a little bit. In fact, 20 of the 49 respondents forecast a rise.

Ebenezer Scrooge was a mortgage banker, and the arguments I am about to marshal for a hard landing in housing might sound un-Christmaslike. But during the just-pricked bubble, it wasn’t the Scrooges and the Marleys who lent more than 100% of the purchase price of a house without bothering to verify the income or employment of the applicant, or even to insist that he or she pay down a little bit of the principal now and then. House prices soared on the wings of the modern, optimistic, growth-obsessed mortgage industry.

All can agree that the housing data are grim enough today. From their recent respective peaks, single-family home sales are down by 15%, single-family housing starts by 35% and single-family home prices by 3.5%. The question is whether the stock market and the famously resilient U.S. economy will continue to shrug off the bad news.
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The fundamental problem, Gordon observes, is that the typical American home buyer can’t afford a home at today’s prices. “We Americans have tested the limits of affordability over the past five years,” he says. “Since the end of 2001, disposable personal income is up about 25% and mortgage rates are little changed. That argues for 25% higher home prices. Instead, home prices rose by an average of 50% and in many markets by 100% or more.” In fact, according to data compiled by Yale economist Robert Shiller, inflation-adjusted house prices in the past five years logged the second-fastest cumulative growth since the administration of William McKinley 110 years ago (the late 1940s hold the record for the fastest rise in real house prices over a half-decade).

Falling house prices in isolation would constitute no grave peril. A housing-induced downturn in job growth is what would cause a bear’s pulse to race. Gordon insists it’s coming, because the formerly potent stimulus of above-trend borrowing growth is about to be removed. Consider, he notes: “Americans pulled out nearly $500 billion of equity in their homes last year in order to buy other stuff. That number shot up from about $100 billion in 2001.” The source of this borrowing? Why, the 12%–or $2 trillion–bump-up in the appraised value of the 2005 U.S. housing stock, double the 2002 increase. Reduce or reverse this appreciation and you stymie the borrowing boom.
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Already, despite a still low jobless rate, delinquencies, foreclosures and other signs of distress are surfacing in the subprime segment of the nonagency market. Even a mild business downturn could cause a revulsion against the kind of easy credit that put so many houses within financial reach (or seemed to).