In the past several months, Google has undertaken a major effort to improve the quality of its index.

From cracking down on high-profile retailers using black hat and grey hat SEO techniques to algorithm updates designed to weed out low-quality content farms, there can be little doubt that Google is serious about changing perceptions about its dedication to quality SERPs.

And Google’s effort continues. Yesterday, the search giant announced that it rolled out its “high-quality sites algorithm” globally to all English-speaking users. It also announced that it’s incorporating feedback provided by users into its algorithm.

From the Google Webmaster Central Blog:

…we’ve also incorporated new user feedback signals to help people find better search results. In some high-confidence situations, we are beginning to incorporate data about the sites that users block into our algorithms. In addition, this change also goes deeper into the ‘long tail’ of low-quality websites to return higher-quality results where the algorithm might not have been able to make an assessment before.

The impact of these new signals is smaller in scope than the original change: about 2% of U.S. queries are affected by a reasonable amount, compared with almost 12% of U.S. queries for the original change.

According to Google, “the algorithm is very accurate at detecting site quality.” That’s quite an interesting claim given that the search engine only just recently launched its blocking functionality.

While publishers will certainly be weighing in on these updates in the coming days and weeks, Google is sending a strong message by going from a roll out of blocking capabilities to incorporating blocking as a ranking signal.

In the past, Google seemed to take a more measured approach to updates, and given the obvious potential for competitor abuse of blocking, it’s somewhat surprising that it has publicly revealed that it’s using blocking as a signal now.

Google’s drive to boost the quality of its index is of course a very good thing in principle, and publishers focused on providing high-quality content will hope that the changes reward them for their efforts.

At the same time, however, one has to wonder if the speed at which Google is changing its algorithms and its desire to publicize those changes is motivated more by a genuine desire to improve the SERPs, or by a genuine desire to create the appearance that it is.

One thing is certain: Google is keeping publishers on their toes, and will probably continue to for the foreseeable future. Those who aren’t totally dependent on the search engine will probably sleep better.