When Facebook (NASDAQ:FB) set up a mysterious press conference this week, everybody wondered what wonders the social network might introduce. Could it be the long-rumored Facebook phone? A steroid treatment for its anemic advertising muscles? The tag line for the even was, "Come see what we're building" -- could Mark Zuckerberg play a literal joke and unveil plans for a new corporate campus?

The answer is, of course, "none of the above." At best, we're looking at a slight boon for ad sales -- but at the cost of scaring away millions of active Facebook users.

The freshly unmasked Graph Search feature looks like a cross between Facebook's deep reserves of user data, Google's information search skills (including contributions from a host of ex-Google employees), and some sleazy online dating service. The end result of this unholy crossbreeding looks like a stalker's best friend.

The tool gives you unprecedented access to public Facebook data. The design idea is simple and makes plenty of sense: Make it easier to find Facebook-hosted information that meets your needs or answers your questions. Example queries include benign searches such as "people who live in my city," or "music my friends like."

More marketing-oriented searches point to the money-making potential of a proper Facebook search tool. "Restaurants in London my friends have been to" sounds like a golden opportunity to insert results at the top of the list -- for a fee. So far, so good. Facebook has been looking for ways to make more money, particularly on mobile devices, and Graph Search fits the bill.

But this thing will also raise an outcry from privacy advocates. More to the point, regular users will quickly find their Facebook data exploited in entirely new ways. Marketers will go crazy at first, and nobody wants to drown in advertising at every turn -- no matter how precisely personalized the marketing messages may be. Stalkers (both current ones and wannabes) just got a huge helping hand.

Sure, you can lock down your information sharing, but studies show that most people never change software settings of any kind. Microsoft gives users a plethora of adjustable controls in its market-defining Office suite, but 95% of users never change a single setting. They do, however, walk away from creepy or inconvenient services in droves. That exodus will be the beginning of the end of the Facebook fad.

This search tool raises more questions than it answers.

Fool contributor Anders Bylund owns shares of Google, but he holds no other position in any company mentioned. Check out Anders' bio and holdings or follow him on Twitter and Google+.

The Motley Fool owns shares of Google and Facebook. The Fool has bought calls on Facebook. Motley Fool newsletter services have recommended buying shares of Facebook and Google.Motley Fool newsletter services have recommended creating a synthetic covered call position in Microsoft. The Motley Fool has a disclosure policy.

We Fools may not all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors. Try any of our Foolish newsletter services free for 30 days.