How the Panda Update Changed the SEO Playing Field
The goal of Google's Panda algorithm was to improve search quality and the process of online information retrieval. It was effective, but hurt many web-based businesses and changed the landscape of SEO, making many in the business re-evaluate their SEO strategies.
As some have noted, search quality has improved, but other algorithm updates, such as the Vince update, have not done much to improve apparent search results. Authority signals tended to provide good metrics for head terms, so established brands did okay.
Recovering from the damage wrought by Panda takes a long time, 30 days or longer, as there are no manual exceptions, and once a site has been penalized, the penalization cannot be overridden. Along with typical on-page optimization, link and authority metrics, Panda adds content quality and credibility, as well as trust metrics.