The truth about blog comments
Blog commenting is probably the most popular – and in many cases, most irritating (because of spammers) – technique of getting permanent links.
The Google PageRank algorithm implies that the more outbound links there are on a page, the less authority or power this page can pass to each of those links. That’s because the page’s PR is distributed evenly between the outbound links. If a webmaster wants to add an outbound link, but doesn’t want Google to follow that link or for PR power to be passed on to the linked page, then that webmaster has to add the ‘nofollow’ attribute to the link. Many bloggers do so to prevent their PR from flowing to the pages cited by commenters. However, this practice is no longer encouraged by Google.
A few weeks ago Matt Cutts blogged about a change in the PR algorithm concerning Google’s approach to passing PageRank through the links with the ‘nofollow’ attribute. Although no PageRank and anchor texts are passed through such links, they are also counted when sharing the outgoing ‘link juice’. The only difference is that it’s neither passed to the linked site nor kept on the page. This means Google disapproves of the practice of using the rel=nofollow attribute for the purpose of not sharing PageRank.
If you own a blog, setting up the ‘nofollow’ attribute to all comments means conserving your blog’s ‘link juice’ and getting fewer comments. The ‘do-follow’ principle can lead to more spam, but it’s a good way to attract webmasters to your site. On the other hand, if you are a webmaster trying to obtain more links by commenting on blogs, don’t rely solely on this method of link popularity improvement. Use a combination of methods, including the time-proven ways of press releases, articles and site submissions to relevant lists and directories, and the newer techniques for site promotion in social media.