SEOs sometimes have knowledge and they do not know where the source of that knowledge came from. Sometimes facts have been known for so long that they are just a part of the fact pool, but we no longer remember where we got the facts and have no way to back them up anymore. So it is always nice when we get a fact re-validated from the search engines themselves. A recent quote from Marissa Mayer (product manager at Google) does just that regarding the number of factors that Google uses in its algorithm. SEOs have known for a long time that Google uses more than 100 factors in determining SERPs ranking. This quote from battellemedia.com/archives/000966.php revalidates the fact.
When asked, How does the Google Desktop Search do ranking on a person's hard drive?, Marissa Mayer answered:
The default rank is by date. (When we tested, we learned that) people understood the context of "when they did see this"? The results list the last time you accessed any particular document. However you can also sort by relevance. The desktop relevance scheme lacks Pagerank (of course), but it does incorporate the other 150 factors (Google uses on the web) - factors like are the (keywords) together, in bold, related, things like that.
Note that although the discussion is about the Google Desktop Search, the comment in bold relates to the search algorithm Google uses for its web search.