I realize this is a topic that tends to be polarizing and arouses very passionate responses from many people, however, I would ask that this be looked on only in the context of a feature request. Not regarding any issues around content or censorship.
Currently, blog authors on WordPress.com are unable to use the established rating systems from icra.org, rsac.org, and safesurf.com to indicate appropriate ratings on posts and pages without resulting to hand-coding individual posts, and/or making some customized CSS changes to pages. While bloggers can have the blog marked as mature content, and limit its visibility on WordPress.com, bloggers do not have a good tool to try to work with rating systems. Code for the above rating systems maybe placed in text widgets, but this is not intuitive, nor always practical, and serves to place the entire content of the blog in the most restrictive rating, when that rating may only be appropriate for one post.
While not a fan of rating systems, and well aware of the trend for tags to supersede ratings, I understand there are those who do prefer to use them as a tool. I would ask WordPress.com in a future version, to allow blogs that choose to be considered dealing with mature subjects, the option of applying content ratings to individual pages and posts via an option box.
Also, I wholeheartedly endorse the efforts to have Dr. Mike cloned repeatedly in the interests of scientific discovery until the ratio of one Dr. Mike for every four WordPress bloggers is reached.