The July issue of Wired includes an article about fanfiction. It traces the history, back into the Star Trek days, notes that it's a common activity of burgeoning writers, and comments on the various fics about the motorcycle of Sirius Black, who the reporter deems "a minor character in the Harry Potter saga".
[Fanfiction's] popularity represents the broad roots of a new literary trend. Witness Wicked, Gregory Maguire's magnificent retelling of The Wizard of Oz. Similarly, authors Francesca Lia Block and Donna Jo Napoli have turned tweaked takes on classic tales into hit books. The kids coming up with today's fan fiction were born using the Web; for them, mixing and matching media is second nature. They'll go on, if they choose to tell great stories. Even if they're all based on Xena: Warrior Princess.