Fanfiction: Do you love it or hate it, or are you totally indifferent? Why?
I wrote my first fanfic when I was something like five years old, about Bambi; I went from there to Star Trek, Robin Hood, Star Wars, and many others. I think it's a natural part of the creative impulse. However, I also think it's a phase that writers go through and eventually must get past if they are serious about their craft. shockwave77598's response to this topic described fanfic as "training wheels for writers," and I think it's a good analogy. When I realized that no matter what I wrote, it was never going to be "mine" as long as it was based on somebody else's work, my interest in writing fanfic dried right up. 
When it comes to reading fanfic, I don't much care for it, but that's because so much of it is the same stuff that every teen or young adult goes through, dealing with all the same issues. Fanfic, much like poetry, is something to be written, not something to be read.
I generally see "property tie-in" fiction, "posthumous sequels," and similar ventures as being little more than "professional fanfic," and don't care for most of it, either.
 I do still actually dabble in a bit of writing that could be considered fanfic, as it's short bits of fiction related to my Star Wars or Call of Cthulhu RPG campaigns. But in these particular cases, it's there to serve the game, rather than as an end in itself.