We previously commented here and here on the famous JibJab parody of Woody Guthrie's "This Land Is Your Land."

Joanna L. Ossinger has a nice article, "The Problem with Parody," in The Wall Street Journal, February 13, 2006.  She notes that some parody sites, including JibJab, end up on both sides of the copyright protection issue, fending off infringement claims from the original owner, and also pursuing infringement claims against sites copying their parody.