Real estate Web site Zillow.com announced last week a major expansion and upgrade to its database of nearly all homes in the country. Zillow also announced it has dramatically expanded and improved its Zestimate algorithm, incorporating 20 times the number of statistical models than before. The new Zestimates are purported to be 12% more accurate than before. Zillow now covers 88% of all homes in the U.S. and has Zestimates on almost 75%. Read the press release here.