Google updates its key search algorithm
Matt Cutts just announced that Google is rolling out v4.0 of its Panda search engine algorithm.
Google runs a number of concurrent search ranking algorithms and periodically updates them all. For example, the "Penguin" algorithm is aimed at decreasing the rank of websites that use artificial link schemes. "Hummingbird" is all about understanding context - the true intent of the searcher.
The "Panda" algorim is primarily concerned with lowering the rank of low-quality websites, and conversely improving the rank of high-quality sources. Previous versions of Panda had the noticable effect of moving news sites and social networking links up the ranks. Sites with lots of advertising, however, found themselves cut adrift.
One effect of recent algorithm changes has been the increasing isolation of all those "snake-oil" SEO salespeople. And that's got to be a good thing. Google is never specific about the criteria it uses within its algorithms. It gives us general guidelines about what makes a website good in its eyes, but web publishers are largely left to trial-and-error in their efforts to scale the search engine ranks.
Being a major point release, it's anticipated Panda v4.0 will introduce fairly large changes. ~7.5% of English sites should experience a noticeable change in rank. Will your website be affected? Only time will tell.