Info from Google itself (or the guy in charge of search quality).
For something that is used so often by so many people, surprisingly little is known about ranking at Google. This is entirely our fault, and it is by design. We are, to be honest, quite secretive about what we do. There are two reasons for it: competition and abuse. Competition is pretty straightforward. No company wants to share its secret recipes with its competitors. As for abuse, if we make our ranking formulas too accessible, we make it easier for people to game the system. Security by obscurity is never the strongest measure, and we do not rely on it exclusively, but it does prevent a lot of abuse.
The details of the ranking algorithms are in many ways Google’s crown jewels. We are very proud of them and very protective of them. By some estimate, more than one thousand programmer/scientist years have gone directly into their development, and the rate of innovation has not slowed down.
But being completely secretive isn’t ideal, and this blog post is part of a renewed effort to open up a bit more than we have in the past. We will try to periodically tell you about new things, explain old things, give advice, spread news, and engage in conversations. Let me start with some general pieces of information about our group. More blog posts will follow.
Interesting (if somewhat general) stuff.