Zillow.com has increased the number of homes that it collects information on and improved the accuracy of its online home valuations, known as Zestimates, by a national average of 12 percent. The Seattle company, backed with $87 million in venture funding, said it now has data on 80 million U.S. homes and valuations on 67 million of those homes. With an estimated 91 million homes in the U.S., Spencer Rascoff has some information on more than three-quarters of the homes in the country.

Zillow has received criticism over its valuation model, with many homeowners complaining that the service wildly misses the mark.

In order to improve the accuracy, Zillow has added new statistical models, including information that homeowners' have added to the site about bedrooms, square footage and other home details.

Spencer Rascoff, chief financial officer and vice president of marketing at Zillow, said the valuations will keep improving as more information arrives from home owners. In Seattle, the company showed a 7 percent improvement in its home valuations.

"We feel like we now have the three legs of the stool of a successful real estate site pretty well established," said Rascoff. "We have valuations, listings and community input and probably the most important foundation upon which our brand is built is valuations. And with this new release we have taken great steps at trying to solidify that one."

Zillow still has no valuation information on homes in South Dakota, Maine, Mississippi, North Dakota and Vermont, but it has added 11 new states to the mix. Some states, such as Texas, also continue to have spotty valuation data.

Zillow also is announcing an agreement today with Yahoo Real Estate and Trulia to create a set standard by which real estate brokerage firms can submit their listings to the Web sites.

It also just signed an agreement to pick up for-sale listing information from Prudential California/Nevada/Texas Realty, a deal that could deliver about 3,500 listings daily. It also struck a partnership to receive about 500,000 daily listings from Network Communications.

Rascoff said the company has a goal to reach 1 million listings by the summer of 2008, a milestone that should be easily attainable given that it already had about 400,000 listings on the site prior to today's agreements. There are about 4 million homes for sale in the country.

"It is a local game. I think we probably need at least 20 percent of the listings in a given city or 20 percent nationwide before we can credibly say that a buyer in that market needs to use Zillow because of our listings as well as all of the other information that we have. So, we are not there yet nationwide clearly, but I feel pretty good about getting there."

With today's upgrade, Zillow is officially leaving the beta period for the Web site.