The engine is designed to provide users with answers to natural language queries and to match phrases and objects on the site instead of just keywords. For example, users can submit a query to find out people they know / may know that work at / live in / like a specific business / city / organization / etc, and that's just a small part of it.
Search results they will receive will be based on both content and relationships.
Graph Search is still a work in progress, but this is a perfect moment to review privacy settings on your account if you don't want potentially embarrassing things about yourself to be accessible to anyone.
I strongly advise you to check out an item we have recently compiled about the privacy implications of Facebook Graph Search, which details not only the issues that may arise for you as a private person and as an employee, but what changes to make to your settings.
If that's not enough, check out Facebook's Help Center and this informative article on how to protect your privacy from Facebook's Graph Search put together by the EFF.