Penguin is interesting because unlike Panda this update appears to be targeting bad SEO practices. Panda was just trying to sort Websites into "high quality" versus "low quality" whereas Penguin is trying to improve Google’s enforcement of its spam policies. Panda went after Websites that were "Not Spam" in nature – just providing the bare minimum of value to visitors. Penguin went after Websites that were (perhaps in some cases unintentionally or unwittingly) crossing the line and putting too much emphasis on doing things to please the search algorithm.