Zillow marketplace is a free service that hooks lenders up with borrowers. Borrowers submit just the essentials - what type of loan they need, where they're located, their estimated property value, their credit history, etc - without divulging any of their contact info. Then certified lenders make offers that can be compared side-by-side. It's up to the borrower to reach out and contact those lenders, not the other way around as it is with services like Lending Tree.
Zillow cites a Harris Interactive study showing that it's more important for borrowers to keep their contact info private than to find the best rates.
According to the company, Zillow attracts about 5M unique visitors monthly, 1/5 of which are looking for a loan and 2/3 of which are looking to buy or sell a home. We've also been told that 1 in 3 professional lenders visit Zillow every month. This traffic is therefore a natural fit for a service like this, which shouldn't have a problem gaining traction.
Some other fun facts about Zillow: of the 90m homes in the US, 80M are listed in Zillow and 70M have estimated prices ("zestimates"). A full 45% of the 90M total homes have been looked up on the site; in San Francisco that percentage is around 90%.