Ted Ives recently authored an article entitled “What is a Link Really Worth? Part 1: Valuing PageRank”  that was published on Search Engine Land, a go-to reference point for online marketers.
Everyone would agree that links are an important ranking factor in SEO. And typically, inbound links from sites with a higher pagerank (PR) are assumed to be worth more than those from sites with a lower PR. But by how much?
Ted notes that Toolbar PageRank is a logarithmic measurement and previous research suggests that each incremental PR level is worth 5.5 times the previous level (e.g. a link from a PR6 site is worth 5.5 PR5 links.
He then conducts a study of his own to measure the correlation between a site’s PR and the number of inbound links. His results are quite remarkable and should help any SEO value the amount of effort required to obtain a link at different levels of Toolbar PageRank.
For a more thorough overview of the value of inbound links  and a complete explanation of Ted’s research on the topic, make sure to check out his article on Search Engine Land.