Google decides to be more open about their ranking systems: “PageRank is still in use today, but it is now a part of a much larger
system. Other parts include language models (the ability to handle
phrases, synonyms, diacritics, spelling mistakes, and so on), query
models (it’s not just the language, it’s how people use it today), time
models (some queries are best answered with a 30-minutes old page, and
some are better answered with a page that stood the test of time), and
personalized models (not all people want the same thing).”