Smashing Magazine wrote:PageRank is only one of numerous methods Google uses to determine a page’s relevance or importance.

Google interprets a link from page A to page B as a vote, by page A, for page B. Google looks not only at the sheer volume of votes; among 100 other aspects it also analyzes the page that casts the vote. However, these aspects don’t count, when PageRank is calculated.

PageRank is based on incoming links, but not just on the number of them – relevance and quality are important (in terms of the PageRank of sites, which link to a given site). PR(A) = (1-d) + d(PR(t1)/C(t1) + … + PR(tn)/C(tn)). That’s the equation that calculates a page’s PageRank.

Not all links weight the same when it comes to PR.If you had a web page with a PR8 and had 1 link on it, the site linked to would get a fair amount of PR value. But, if you had 100 links on that page, each individual link would only get a fraction of the value.Ranking popularity considers site age, backlink relevancy and backlink duration. PageRank doesn’t.

Content is not taken into account when PageRank is calculated.
PageRank does not rank web sites as a whole, but is determined for each page individually.
Each inbound link is important to the overall total. Except banned sites, which don’t count.

PageRank values don’t range from 0 to 10. PageRank is a floating-point number.
Each Page Rank level is progressively harder to reach. PageRank is believed to be calculated on a logarithmic scale.
Google calculates pages PRs permanently, but we see the update once every few months (Google Toolbar).