According to a new report put out by Deutsche Bank, half, or approximately 25 million homeowners will be underwater with their mortgage by 2011, the year in which Deutsche Bank expects home prices to finally stabilize.
Les Christie and CNNMoney.com are reporting that the Deutsche Bank forecast goes further than any other estimates that have been calculated to date, "First American CoreLogic estimated 11 million homeowners -- and rising -- were underwater by the end of 2008. Moody's Economy.com estimated 15 million at the end of March and projected 17.5 million by early 2010. Zillow.com reported that 20 million were already underwater at the end of the first quarter 2009".
There are two reasons this phenomenon of being underwater with a mortgage, also known as zombie homeowners, is significant. First, owing more than the house is worth will negatively impact consumer behavior and spending. We are seeing this already.
And second, home value declines lead to more foreclosures, and more foreclosures lead to more losses for the banks. According to Christie's article, "Currently, 26%, of defaults are classified as strategic, according to a recently published paper by Paola Sapienza, a finance professor with Northwestern University, and Luigi Zingales, a finance professor at the University of Chicago." In other words, the homeowner voluntarily walks away from the property rather than continuing to pay interest on a loan that far exceeds the value of the property.
So while Wall St. and Jim Cramer celebrate the fact that home sales may have bottomed, the much bigger problem is that the strained relationship between the demand and supply for real estate means that home values are still falling. There is insufficient demand for real estate to stop home values from deteriorating further.

If the report is accurate, we are going to see further declines in the market. I honestly couldn't imagine being so upside down on my mortgage that I would walk away from it. However, I never bought more than I could afford and never put personal expenses on my home equity line.