Google recently made far-reaching changes to the way it ranks search results, and the search marketing community has been abuzz with tales of woe ever since. Some have speculated that the key to understanding Google's latest is that they've applied some sort of test of "commerciality" to certain phrases, roiling the waters for sites ranked well on those phrases, and leaving non-commercial phrases more or less alone. The idea is that this would cause a stampede of site owners over to the paid AdWords program, or at least making the point that Google isn't up for providing a free lunch to clever "SEO-ized" sites indefinitely.

…read on in Cracking Google s New Algorithm by Andrew Goodman