Not only is Facebook the online destination where users spend the most time, it also represents a massive global repository of marketing data. Companies have spent the past few years trying to understand how to leverage Facebook Pages, Likes, and other aspects of the social network in order to connect with customers and gain tactical advantage over competitors. Facebook’s Graph Search, announced this week, seems to offer brands a new tool for mining the market research data stored on its servers.

The new feature lets you search the interests, location, and preferences of your friends. This will initially cover four categories – people, places, photos, interests – and gradually expand to cover all content, Zuckerberg said at the official announcement. “Graph Search is a really big project. Eventually… we want to index all the posts and all of the content on Facebook. I thought it couldn’t be done. This is just some really neat stuff. This is one of the coolest things we’ve done in a while.”

He and fellow executives showed how users could discover previously overlooked photos and posts and “likes”. Tom Stocky, a former Google employee, showed what appeared to be a market researchers’ dream tool: the new feature allows users to ask, for example, what TV shows are most liked by doctors (Grey’s Anatomy, House, The Doctors), or software engineers (Big Bang Theory).

One thing Facebook is being particularly quiet about is the potential revenue that will result from the new search functionality. The act of conducting a search on Facebook is a powerful expression of interest, and as such, an expression that advertisers would love to capture and use. For example, if a user searched for “books liked by my friends,” a publishing company could pay Facebook to place ads for books on the user’s Facebook page.

Commentators have predicted that advertisers might eventually pay Facebook for users’ search data, and then use that to place advertising in front of the user on another site using cookies. Now a publicly traded company, Facebook continues to look for new ways to make money from the huge amount of personal data stored in its servers.

The service is in early beta, and is not yet widely available, but the concept has some valuable implications for businesses on Facebook.