One of the most heated topics on this blog has been the existence or non-existence of a shadow inventory of unsold homes. The real estate firm Zillow purports to have proof that such a parallel universe of marketable homes exists. Here's a key section of the article from Zillow veep Stan Humphries:

This “shadow inventory” will likely be one of the contributors to a recovery that is more “L”-shaped than “V”-shaped. As sales rise and inventory is cleared off, many homeowners will start to test the waters again by putting their homes on the market, thus keeping supply levels higher than they would be without this pent-up inventory. These sustained supply levels will serve to keep downward pressure on prices, which can only increase as demand begins to outstrip supply.