A lot of us know about the recent letters G sent out concerning "unnatural backlinks" and also news about private blog networks closing their doors and getting individually hit... some of the people reporting receiving the letter have talked about using blogroll and footer links, and private blog posts. G knows these type of links cause the most SERP manipulation, and also that they are the smallest in number compared to the other backlinking methods, so the easiest to detect. And while blog comments and profile links are sometime legitimate, high PR links buying is only for one thing. It's harder for them to penalize sites that are getting blasted to (although on new sites, where no competitors even know about it, they do penalize) because negative SEO would be too easy. And high PR links, you have to buy, and G has spoken out against paid backlinks for the longest, and is rolling out stronger detection of them. But they aren't targeting all blogroll and other sitewide links. Lots of legitimate and popular sites have those. They appear to be going specifically after the services selling them and scraping the urls in the network. There will be a rise in actually private private blog networks, and people making there own. A question still out is whether this applies to blog posts, which stay on the frontpage for only a day or so.