An excellent, wide-ranging piece. I like some of the officially sanctioned fan fiction, like the new Sherlock Holmes or Bond stuff by Anthony Horowitz. I generally avoid fan fiction, though I do occasionally indulge in my own outlined rewrites of missed opportunities (the Star Wars prequels for instance).

A couple of my personal "fan fiction" favourites: Wide Sargasso Sea (a fine Jane Eyre companion piece) and Rosencrantz and Guildenstern Are Dead (an amusing tragicomic play, featuring Hamlet's doomed University pals).