SEO: Link Analysis, Web Spam, and the Cautious Surfer is a great look at how pages can be ranked by analyzing how random or cautious surfers might end up at a given page.This goes outside what a search engine can do by spidering pages, I think. It goes into the behavior of people in their surfing. What links do they follow?
Now the question is who would you give that information to? You give it to whoever's toolbar you have installed! Ouch!
In return what do you get?