Following up on the previous post, Zillow also announced today that it has gotten together with Yahoo! Real Estate, Trulia and a handful of others to establish a standard format for home listings. This is hoped to lower the barrier and make it easier for real estate agencies to list properties online.

Network Communications Inc., the largest U.S. publisher of local print and online magazines for the real estate market, also announced today that it will join Zillow’s Listings Feed program and feed it 500,000 residential listings daily.

For Zillow, banding together with other online real estate players with a common listing format seems to represent a move to draw more listings away from traditional offline sources and grow the overall online listing pie.

More listings also mean a better value proposition for users, which in turn means more traffic and user participation (both home buyers and sellers). This user participation, according to Zillow CFO Spencer Rascoff, will be the No. 1 factor in continuing to improve Zestimate accuracy.

“The next big untapped area of improvement for us is the wisdom of the crowds,” says Rascoff. “Every home you see on Zillow, whether it be your house, your parent’s house, your neighbor’s house, I know you have an opinion on whether or not that Zestimate is right. About 400 million Zestimates have been viewed and that’s a lot of opinions that can improve accuracy if we can harness them.”

All these factors also work toward increasing inventory and the value proposition to advertisers, set forth in the October launch of Zillow’s ad product, HomeDirect.

“Everything that we do on the consumer side is about increasing unique visitors and levels of engagement,” says Rascoff. “This lets us drive more page views and more time on our site in order to have more ad inventory to give back to our advertisers.”