For years the most expensive place to live in New York City had been the Upper East Side, along Central Park. If your mail boasted the ZIP code 10021, you knew you had officially "arrived." That is, until the U.S. Postal Service changed things up.
In 2007, the post office split the posh ZIP code into three parts, adding 10065 and 10075, respectively. U.S. Rep. Carolyn Maloney cited population growth: There were just too many people getting mail in 10021. It was a nightmare for the post office. Suddenly notable residents like media giant Rupert Murdoch and novelist Tom Wolfe were no longer living in the most sought-after ZIP code in America [sources: Roberts, Shapiro].
As in life, wounds heal with time. In fact, those who kept the posh ZIP code might want to consider moving a few blocks: the new 10065 placed seventh on Forbes' 2010 most expensive ZIP codes list. As for 10021, it lags behind at No. 25.
Your address certainly does affect your home's value. How it affects it is another matter. The education and crime -- or lack thereof -- associated with your address is obvious, as is the quality of your streets and the property upkeep of your neighbors. In addition, there may be unique issues that come to bear on your home's value (an Internet behemoth is born next door.) Research issues within your power and maintain a dialogue with local residents to give you the best chance of learning about unexpected developments.
Even in a tough market, if you think you're home will never regain its value, keep your eyes open. Change may be on the way. Who knows, your neighbor's kid could be creating the next Google.