“Y’see, the Web is full of people like you and me, making links between documents; human beings, making decisions about documents, voting with their links. When I link to some arbitrary document, it’s an indication that I think that it’s in some way authoritative. When you link to a document I wrote, you’re indicating that I’m in some way authoritative. The Internet is already structured in a meaningful way, but that structure is obscured. Google teases out the relationship between the URLs, examining the webs of authority: this person is linked to by 50,000 others, and he links to this other person over here, which indicates that person one is a pretty sharp individual, one who’s inspired 50,000 human beings to take time out of their busy schedules to link to him; and person one thinks that person two is on the ball, which suggests that person two knows what she’s on about.”
http://oreillynet.com/pub/a/network/2002/03/08/cory_google.html