Google doesn’t trust all links
In O’Reilly Radar > Search Engine Spam?, Tim O’Reilly addresses concerns that their network of sites, which includes Perl.com, XML.com, and others, is “selling PageRank” via text link ads.
As Danny sullivan points out in his comments, a lot of companies (including the former owner of Danny’s Search Engine Strategies conference) are selling the same type of advertising, cashing in on the economy created by search engines’ reliance on anchor text to generate search engine rankings.
Google engineer Matt Cutts chipped in to support the use of the rel=nofollow attribute on ad links. He also stated that he had been aware of O’Reilly’s link sales for some time, and that “parts of perl.com, xml.com, etc. have not been trusted in terms of linkage for months and months.” Further, that “just because a site shows up for a ‘link:’ command on Google does not mean that it passes PageRank, reputation, or anchortext.”
Those words, if they are heard throughout the SEO world, are sure to shake the confidence of many text link brokers… it’s about time. Smart link traders will be moving toward a model that makes it easier to use their networks for advertising that isn’t solely targeted at spiders.