One of director Federico Fellini‘s great works is 8 1/2. It is a movie about making a movie, something film critics call a mirror. (In fact—since it is more precisely a movie about a Fellini-like director making a movie about making a movie—it is actually a double mirror.) This technique of using a medium to explore that medium can prove quite insightful.
Although the exercise doesn’t seem to have continued, the Infinite Regression Awards appeared again this year. The “Reggies” were originally handed out in 2001 and repeated in 2003 to recognize examples of mirrors used on the Internet. This is where one can find a blog about blogs or a forum about forums. Mirrors also exist for wiki about wikis, search about search, and a mailing list about mailing lists. The Internet itself is considered a network of networks. For the 2007 version, the committee (of one?) has added Wikipedia about Wikipedia and Google about Google.
I think it would make for an interesting study to analyze these kinds of Internet mirrors to see what they tell us about the strengths and limitations of different media channels.