Google have recently filed United States Patent Application 20050071741 on March 31, 2005. In which many of the search giants secret ranking criteria is revealed and it makes very interesting reading. You have got to read this if you're serious about ranking well in Google. The days of Spaming Google are drawing to a close. With this patent they reveal just how hard they're coming down on Spam sites.
Google takes many steps to filter out spam site, while spam sites try as hard as possible to get Google to fall for them. It is interesting to see what matters in Google ranking where they are trying to lower spam site rankings while raising valid websites’. For example:
Because the majority of Spam websites only register a domain name for one year. A domain registered for a longer period implies that the owner is more likely to be legitimate and serious about their web site.
This is just one of the unusual factors now considered by Google when indexing and ranking a website. Factors you could never even have guessed at in some cases.
Sites can be ranked seasonally. A ski site may rank higher in the winter than in the summer. Google can monitor and rank pages by recording CTR changes by season.
There are many factors that go into Google search rankings, that is why they are so good at what they do.