a good article in The NYT on google's search algorithm. a must read for those who are interested in knowing how the google search engine works.

Google Keeps Tweaking Its Search Engine

here's my quick summary:

a. google's impressive tracking system traverses through all of internet's web pages and indexes them. they, therefore, know exactly where, what kind of information is available
b. Signals, as google calls them, 'involves more than 200 types of information' which rank web pages
c. These signals in turn feed Classifiers - formulae that infer about the 'type of search' from the search terms
d. these classifiers & signals in turn measure the relevancy of a web page. the more the diversity on the page in terms of content, the better its rating