The Highlight smartphone app, which alerts users when their friends are in proximity, must be accessed through a Facebook account, even though in theory it could work independently of Facebook.

WSJ: Corrections & Amplifications

The theory here is that search results are relevant because it is related to your friends, their personal proximity, their friends, the things they do, where they do it and in general their wants and likes.

FORBES: Facebook Graph Search no Threat to Google.... Yet