It has been nearly six years since U.S. home prices peaked and then plunged, and still the nation’s mortgage markets remain mired in slump. Despite occasional signs of improvement in some localities, the S&P Case Shiller Index shows home prices down 9 percent from their previous post-bubble high – itself very low in relation to trend. Meanwhile a backlog of some 400,000 homes awaited liquidation at the end of 2011, and an additional 2.86 million mortgages were 12 or more months delinquent. That’s a “shadow inventory” of 3.25 million homes already foreclosed or now facing foreclosure – an inventory that weighs on home prices, families and neighborhoods alike.