Sarah Lacy describes Glassdoor's use of Facebook to grow rapidly:

So back in April, it launched something called Inside Connections on top of Facebook. It’s a service that allows you to see if you know anyone who knows anyone at a company you might be researching about a job. The company spent four years getting to 6 million monthly uniques —  that’s more than doubled over the course of just 90 days, thanks to Facebook. The company had 1.4 million registered users a year ago, and that’s grown to 10 million registered users today. There have been some 400 million connections uncovered by job seekers and 98 percent of new users are signing in via Facebook. “We are adding a user a second right now,” said Robert Hohman, co-founder and CEO of Glassdoor in an exclusive interview with PandoDaily.

Think about that for a minute. This isn’t a new company, so those percentage increases aren’t off a small number of users. This is a four year old company with an experienced management team and deep pocketed investors. Facebook just changed its entire trajectory in a matter of months: How fast it’s growing, where it’s growing and possibly even its fundraising and hiring plans.

The biggest impact? In a matter of days, Facebook propelled Glassdoor — ready or not– into international markets like some sort of daredevil human cannonball. Before the change 20 percent of its audience was non-US; now 40 percent is.

Surprise number three for Hohman: the quality of those users. Glassdoor has always walked a fine line in terms of how much data it gives away without forcing you to contribute or at least sign up. There was a risk that a flood of Facebook traffic might add little to its core user generated product. But content has surged too: The site now has three million company reviews and salary data points from 185,000 companies in 130 countries around the world. A stunning one in five users are actually contributing content. That’s high for any user generated content site.

Growth Hack: Just add Facebook.