As a proprietor of a small, successful niche blog, I can easily share some insight into why Google recently started punishing blogs that have guest posts.
At API Evangelist I get about two offers a week from random companies and individuals asking to guest post on my blog. These people cite several reasons for wanting to do it, ranging from me helping them as an aspiring blogger, to them helping me with more content and traffic. If you know me, you know I don't have a problem producing content, and I do not blog because I give a shit about pageviews.
In addition to these smaller, much frequent requests for guest posting. I also get the occasional bigger company looking to “partner” with me, when in reality they have no desire to partner and generate value for my readers, or move my research forward. These conversations start out entertaining my perspective of partnering and bringing me value, but once I choose to dance with these partners, they almost always start getting heavy handed about me publishing what they want, and providing links to their own sites and content.
My friend Mike Schinkel has a great post on this very topic, echoing much of what I’m saying. Mike is like me, he blogs for himself, not to generate pageviews. I started API Evangelist to help me better understand the API space, and while I do have a mission of also educating the masses about APIs, the primary directive is still about educating myself—without this none of it matters.
The reason Google has begun cracking down is because it is in their best interest to ensure blogs are of the highest quality, unique content possible. What these “guest post farmers”, and the enterprise companies that employ this same practice don't realize, is their aren’t generating any value, they are extracting and diminishing the value of these blogs, and this is what has catching Google’s attention.
On second thought, maybe these companies realize what they are doing. They are just leeches, looking to extract value for their purpose—at all costs. They don't care about your blog, content or career. They want to suck every last page view from your blogs soul, transferring any value you may have had to their operations.