Guest posting is widely recommended as one of the best white hat methods of manufacturing link authority. However, I suspect that the link authority passed by hyperlinks included in the "about the author" sections of guest posts may have already been diminished in value. Further, if this lessening of link authority has not already occurred, then it seems likely to occur in the future.
With guest posts, it is an accepted practice to include back links to the article author's site in an "author bio" paragraph in return for the publisher getting free content to post on their blog. Due to this trading of content for back links generally generating a good user experience for the readers of the guest posts, there was no urgency for Google to modify their algorithm to discount the value of these manufactured links. However guest posting seems likely to be on Google's radar as it has become so widespread and frequently utilized for its value as a free source of backlinks.
The links in the author bio section of guest posts are an artificial method of boosting Page Rank. The links that are being manufactured via guest posting are not a reliable signal of content quality. Just as Google diminished the authority of links from article directories because they were not pointing to the highest quality content on a subject, the links in guest posts may be discounted as being every bit as artificial
The first bit of evidence that I have that the value of guest posting has already been diminished in value is based on a guest post I recently published. My article, Beating Google By Doing Better Than Competing On Price, did not generate a Google Alert for a term that I linked to in the post's author bio section. I created a link to MacDuggal.com in the about the author section, and was mildly surprised not to get an alert for this term. The guest post was on the widely read blog published by SearchEnginePeople. It attracted 40 tweets, which seemingly should be a signal that Google would recognize indicating that it was not a spammy post.
Admittedly, not getting a Google Alert for a keyword term is far from being a definitive sign that links in the about the author sections of guest posts are not passing much link authority Further, a couple of caveats should be applied to any broad conclusions about the link authority of guest posting based on the absence of a Google Alert. My conclusion only applies to the links in the about the author area. Links in the main content area of a guest post seem less likely to have their link authority diminished, as these editorial links presumably point to content that is relevant to the article's subject. Also, the content in the post I wrote was about SEO and not relevant to the content on the site to which I linked (Mac Duggal is a couture and prom dress designer).
An assumption that I am making is that the Google algorithm is capable of determining the section of a blog post that is about the author. The "author bio" section of the post is typically at either the top or bottom of an article and uses descriptive words such as "posted by", "written by", "authored by", or simply "by". Thus, it would not be terribly difficult for Google to discover and discount author links.
Even if the conclusion I have jumped to on what is admittedly thin evidence is correct, it does not indicate that guest posting should be abandoned. Guest posting remains an effective method of reaching a broader audience, building a reputation. and generating clicks to a blog or website. However, the current effectiveness of guest posting as an SEO tactic may be over rated.
I considered submitting this article as a guest post in order to reach a broader audience than the readership of this blog. However, I decided it would be a bit too ironic to guest post to another blog an article about diminished effectiveness of guest posting. If I have jumped to an incorrect conclusion, I may have lost some link authority by not having this post published on another blog, at least for the present. However, I am convinced that author bio links in guest posts are unlikely to be an effective SEO tactic for building link authority in the future.
It will be interesting to keep an eye out for research into the link authority from guest posting. Until more conclusive data is available, it is most likely appropriate to continue guest posting, but with minimal expectations in regard to the link authority doing so is likely to produce.
Blog publishers may want to review their editorial policies in regard to guest posters including links to their own sites within the content of an article. As it seems likely that guest posters will be interested in including links to their sites into the content area of articles, publishers will want to police this activity to maintain the quality of their blogs. However, it may be appropriate for blog publishers to loosen their guidelines a bit in regard to content area links in order to adequately reward their guest posters for providing free content, as long as the links are contextual and lead to information that provides value to the reader.