According to Web measurement firm Compete Inc., Facebook has passed search-engine giant Google to become the top source for traffic to major portals like Yahoo and MSN, and is among the leaders for other types of sites. Being a member of Facebook involves having friends and family share Web links to interesting news stories, photos, videos and Internet sites. This "friend-casting" of information has helped propel Facebook into a major force in directing traffic around the Web.This trend is shifting the way Web site operators approach online marketing, even as Google takes steps to move into the social-media world.