PostRank tracks your blog posts to see how “popular” they are in the larger world of the blogosphere. For example, post about your breakfast, you’ll probably get a low score. Post about something that a large number of blogs are talking about, Susan Boyle for example, and that post will get a much higher score. I’m not saying you should be specifically gunning for higher scores, but at least you can get an idea how your posts score against the larger blogosphere.