Call it the great real estate disconnect of 2010: Mortgage rates have been at half-century lows and home prices have stabilized, but applications for mortgages have declined most weeks during the past three months, as measured by the Mortgage Bankers Association.

Picture this: You've signed a contract to sell your house. Your buyers say they have nailed down the right mortgage. All is well. But then the appraisal comes in low -- $25,000 to $50,000 under what was agreed upon in the contract.

With tougher mortgage underwriting rules a virtual certainty under Congress's financial reform legislation, lenders have begun confronting still another vexing issue: Can homebuyers who have high credit scores be trusted not to pull the plug -- strategically default -- when the economy hits a rough patch and home values tank?