Glassdoor is announcing some significant product news today that leverages Facebook’s social graph to add in references and connections into its already robust job hunting product.

It’s a smart strategic move that makes Glassdoor a whole lot more valuable to job seekers, and at the same time, launches the first real significant competitive volley at LinkedIn in more than a decade.

The company started as a site that collected detailed information on salaries. It drew people to the site with the promise of a voyeristic peak into something social graces and corporate rules usually prevent us from talking about: How much we make.

On top of that, Glassdoor layered in a basic job board to monetize its traffic. And, now, the third layer is social. Glassdoor is now allowing you to see how much people make in the job you want, whether there are openings in the industry and via Facebook, whom you may know who can help you get the job.

Like LinkedIn, the app helps you connect not just with people in your immediate social graph, but people connected to those people. “There’s a huge amount of valuable social graph information about jobs laying fallow in the 800 million records on Facebook and no one has figured out how to capitalize on that in interesting ways yet,” said Rich Barton, chairman and co-founder of Glassdoor in an exclusive interview with PandoDaily.

Sound a lot like LinkedIn? It sounds even more like Zillow three years ago. You know, Barton’s other company that just went public.

Like Zillow, Glassdoor got attention and users by shining a bright light on “something scary, confusing and dark” in Barton’s words, in order to allow people to make better decisions about important things. The team creating Zillow and Glassdoor both spun out of the under-the-radar Expedia mafia in Seattle, with Barton co-founding both.

Both had a strategy of not paying to acquire users, and not trying to monetize them until there was critical mass. Instead, it got users by providing data that was provocative and that didn’t really exist elsewhere before. And then both monetized by layering in pretty commodity listings: In the case of Zillow it was MLS listings, and in the case of Glassdoor it was a basic job board.

All of that isn’t too surprising. Successful repeat entrepreneurs frequently go back to the playbook that worked. What’s surprising is that it appears to be working again. Barton says that Glassdoor’s traffic at 7 million unique users per month is exactly where Zillow was at this point in its trajectory.

The move towards social is something new, and it’ll be interesting to see if that accelerates Glassdoor into an even bigger company.