I consider using e.g. tumblr and blogspot for tier 1 blogs of my PBN to keep the costs of my PBN to minimum, but I'm afraid of one thing: If e.g. Google finds out somehow that you are using your blogpost blog only for linking/SEO purposes, they will ban it. This has happened to me one time. So what would you suggest to avoid getting your tumblr or blogspot banned? Also, which other free web 2.0 blogging services would you recommend?