Google's Content-Quality Panda Guide
Quality content is clear, simple, and easy to understand. It offers elements that educate, inform, enlighten, change impressions, encourage trial behavior, and inspire the readers to take other useful actions. Quality content is now the driver for search marketing, social media, content marketing, inbound marketing — and, arguably, all online communication.
Although the concept of "quality" is somewhat subjective, Google is mostly in the driver's seat — and their new Panda algorithm should help them improve their ability to separate quality content from the pack of also-rans.