If my property value went down, not much. It is paid for and I don't plan on going anywhere, so whatever paper value it has is inconsequential. If anything, it would improve my operating finances as my tax burden would decrease.

If everyone's property values went down, things would look grim. A large segment of property owners are in debt up to their eyeballs and a decline in value can soon see them underwater, putting them on the verge of bankruptcy. Once they feel the trouble they are going to stop buying the goods and services I sell them.