John Scalzi has an excellent look at the new Organization for Transformative Works, which believes that fan fiction is transformative and legitimate. Like Scalzi, I'm sympathetic to the writers and lovers of fan fiction. I also agree with him that this is a looming train wreck. As he says,
If and when a fan, told by, say, NBC Universal to take down her Battlestar Galactica fanfic, decides to make the legal argument that her work is transformative and fair use, thus obliging the corporation to show up in court to make a counter argument (i.e., to throw more resources at the problem than a simple Cease and Desist) and the fan shows up in court with the assistance of an umbrella group dedicated to the proposition that all fan work is legal and transformative, I suspect the era of benign neglect or tolerance of fan activity will be at a sudden and pronounced end. Because now the fans are saying, why, yes, this really does belong to us, and corporations who have invested millions in and can reap billions from their projects will quite naturally see this as a threat. From there it’s all DMCA notices and entire fan sites going down.
This already happened with the late Marion Zimmer Bradley and her support of fan fiction based on her Darkover novels and stories. As her Wikipedia article states, "For a time, Bradley actively encouraged fan fiction within the Darkover universe, but this came to an end following a dispute with a fan over an unpublished Darkover novel of Bradley's that had similarities to some of the fan's stories. As a result, the novel remained unpublished, and Bradley demanded the cessation of all Darkover fan fiction."
If that's what happened to an individual author and her support of derived fan fiction, imagine what a big media corporation will do the first time it encounters a similar situation. Not a pretty picture.