It means that our ranking algorithms have good recall but very poor precision. We value web page connectivity more than its content. We don't know how to teach machines to evaluate web page for its merit so we hope that a large number of Twitting, Liking and Plusing non-experts will approximate single expert. Millionshort shows that this model isn't good enough.
Yahoo became the goto portal because the quality of their links was high. Google overtook them because metadata was the only practical way to keep up with the pace at which the web was expanding.
However, after more than a decade of SEO, it's limitations are evident as the long tail gets increasingly harder to reach with search engines based on the Google model, e.g. "Purchase empiricist philosophers on eBay."
My suspicion is that Google is abandoning neutral search for personalized search in part because of the problems SEO represents when it comes to neutral searching and personal tracking provides an algorithmic way of establishing the quality of results for ranking purposes. One which is easier than attempting to develop a neutral curation algorithm.