Zillow.com today is releasing numbers about its growth for the first half of the year, touting a boost in unique visitors and mobile downloads. The Seattle online real estate company said it attracted 10.7 million visitors in June, up 26 percent over the same period last year. Meanwhile, the company says it has recorded more than 1.75 million downloads of its mobile app across platforms such as the iPhone, Android and Windows Mobile.

But there are key metrics that you won't find in the Zillow press release: profits and revenues. Of course, as a privately-held company, Zillow.com can choose not to release those sorts of numbers.

But at some point -- given the $87 million that's been invested in Zillow over the years -- those numbers will have to become more important.

The 5-year-old company is taking steps to drive revenue beyond its online advertising base, adding rental listings in December and broadening its mortgage marketplace. In fact, the company's mid-year report indicated that borrowers submitted more than 350,000 loan requests and lenders responded with some 4.7 million loan quotes.

The company's directory also is growing, with more than 260,000 registered real estate agents and more than 19,000 lenders. This is all heralded in the release, with Zillow COO Spencer Rascoff saying that the company has become the "leading source for real estate information online" in just a few years.

Now, it will be interesting to see if Zillow can continue to transition from a big community with growing traffic numbers into a profitable business that justifies its lofty valuation.