Domain Registration Length Affects Rankings

How long you register a domain name for impacts its search engine rankings. Pagerank is essentially the first claim of US Patent 220050071741 (which is held by many people including some Google employees). It states:

A method for scoring a document, comprising: identifying a document; obtaining one or more types of history data associated with the document; and generating a score for the document based on the one or more types of history data.

Claim 38 says (my emphasis added):

The method of claim 1, wherein the one or more types of history data includes domain-related information corresponding to domains associated with documents; and wherein the generating a score includes: analyzing domain-related information corresponding to a domain associated with the document over time, and scoring the document based, at least in part, on a result of the analyzing.

And claim 40 specifies some of the domain-related information they are referring to (my emphasis added again):

The method of claim 38, wherein the domain-related information is related to at least one of an expiration date of the domain, a domain name server record associated with the domain, and a name server associated with the domain.

Therefore, amongst the over 100 factors used in determining a page's pagerank and its ranking in search engine results is the expiration date of the domain of the page. Reason suggests more legitimate web sites are committed to their domain names and would register them for the more time than fly-by-night sites. Google sums it up best in the patent's 99th claim (my emphasis added once again):

Certain signals may be used to distinguish between illegitimate and legitimate domains. For example, domains can be renewed up to a period of 10 years. Valuable (legitimate) domains are often paid for several years in advance, while doorway (illegitimate) domains rarely are used for more than a year. Therefore, the date when a domain expires in the future can be used as a factor in predicting the legitimacy of a domain and, thus, the documents associated therewith.