Many of our sites were slapped by Penguin. Their links were from PBNs, comments, blogrolls, profiles, article sites, 301 redirects, etc... But when you type in competitive keywords now, like "unlock iphone" or "buy wow gold", you see sites in the top 10 still openly using these tactics, many with PBNs and homepage links. Many with poor anchor diversity, uneven link velocity, and generally shitty links but in high numbers. Hell, G still ranks sites with the "This site may harm your computer" warning. Penguin is terribly inconsistent, so lets theorize as to why that is. These are some possibilities I can think of, feel free to add to them or shoot them down. Or if you believe Penguin is fairly consistent you can state why. 1.) G's servers, indexing, cache system, computing power, etc.. weren't powerful enough to consistently detect and penalize sites. They will attempt to take care of this in updates. 2.) Too many sites use these tactics, and G can't completely change their SERPs overnight, so they are doing this drip by drip. 3.) G has no intention of disallowing all BH/GH, because these things force more companies with deep pockets to use Adwords. 4.) Penguin was mostly an attempt to discourage BH seo, they put away some sites and made examples of them, but still reward black and grey hat seo. Luck of the draw. 5.) Penguin is designed to go after the sites with the most number of red flags, not all sites with BH seo. i.e. you also need poor on-page, a high bounce rate, poor CTR, etc..