Not only did I write Star Trek fanfics, I had a story arc going.
I tend to think people give fan fiction too much credit these days. Back in the Usenet era people didn’t take fan fiction as seriously and most of it got torn to shreds by other users, passed around, MSTied, ect. Now it’s like some sort of clique where you have to write things a certain way or write a certain amount of Erotica to be popular.
I did have a short stint where I used to write it back in high school, but after a while it felt really lazy to me and I decided I’d rather spend time working on outlines for my own universe and characters. There’s something more rewarding about building your own world as opposed to retreading on familiar ones.
Once in a while I do try my hand at Simpsons or Sonic the Hedgehog fan fiction only to find I cannot make it past the second page because I feel it lacks originality and individuality.
I also tend to restrict myself to the laws of said-series’s own universe, physics, ect. and I not try to make anything too “impossible” happen (Those characters really aren’t attracted to each other, let’s be honest). I like to be believable and convincing with my writing. I tend to write closer in spec script territory but in story format. My whole problem is that I respect other peoples’ material and write within their limits. Maybe that is a good discipline to have, especially if I ever get picked up for a published tie-in franchise.
As for the Star Wars EU, that all goes through George Lucas and approved for the series bible, so it’s not considered fan fiction, no matter what anyone says. You guys can go ask people in the Literature section over at Force.net if you want.
You know what’s really horrible? When a fanfic author is better than the author of the setting they’re writing in. It has happened, although the only real example I can think of are some MSTers who come up with funnier jokes for bad fanfics than MST3K came up with for their bad movies. Oh yes, and some Star Wars authors (it may be approved by Lucas, although I doubt he actually looks over every novel, but fact is it’s Lucas’s setting that someone else is writing for).
Well, I can think of at least one very badly written professionally published Trek novel - War Drums. Just awful, awful preachy stuff. If that’s the standard a fanfic writer has to beat, it’s not a high one.
The story Tiberium Wars is apparently far better than the official novelisation, but that’s more an example of the bad fanfic writer getting hired and inspiring a better fanfic writer to do a better job.
It kind of bothers me when people say this, because I don’t think fanfiction writing is the same process as original writing, nor do they work with the same skill set. Writing fanfiction is about engaging with a text*, and it’s about exploring aspects of the text that aren’t necessarily covered in the source/canon. It’s certainly not ‘easier to write fanfiction’, it’s just completely different. I’m having trouble exactly enunciating what the differences in the process are, and I’ll go see if I can find an article that explains it better.
*Film, TV show, game, boy band interview, whatever.
Well, look at it this way: an original setting requires coming up with a new premise, new characters, new locations, etc., but it may well have the same old story covered hundreds of times. For a recent movie example, look at Avatar. That’s not to say original creations can’t have innovative plots, but it’s not necessarily connected. On the other hand, a (well-written) fanfic reuses familiar characters, locations, and premises, but must have a new and interesting plot to be of any worth. Depending on what a particular reader might value more in a story, this can make fanfic more engaging to them than wholly original works.
I’m not sure I’d call that a completely different skill set though. An author of an original series can also set up those “I see what you did there moments”–he just has to make the characters from scratch first, rather then borrow them. I agree that fanfiction tends to emphasize different things. But it’s still within the same realm, the same skill set of original writing, I think.
I wrote in the Buffy fandom for years, and I’m sure most of it is still floating around out there, though I was just 19 when I started and I know for a fact that I wasn’t very good. Then I dabbled in a few other fandoms like Band of Brothers and Hot Fuzz. Most recently, the majority of my writing has been for the Yuletide fic exchange and Star Trek
There’s a huge market for writing in established francises, except they don’t call it fanfic if it gets published or produced. That’s just the way it works in TV and comic books and genre fiction. What’s the difference between Buffy fanfic, and the writers not named Joss Whedon who worked on Buffy? Then think about Joss Whedon writing for X-Men. And all the syndicate writers who churned out The Hardy Boys and Nancy Drew.
So it isn’t all so hard and fast. The only thing that makes it “fanfic” is if it’s published on the internet, and hasn’t been sold to a corporation. Creatively it’s the same as working in any other established francise.
There’s a blogger out there who hates, hates, hates fanfiction and makes it a point to attack fanfic, the writers, the readers, and everybody peripherally involved at least twice a year. He makes his living as a writer, and he feels like fanfic writers make a mockery of everything he stands for because “they aren’t creative.”
He also writes Diagnosis Murder tie-in novels. Make of that what you will.
Fanfic writer here–I write (or wrote–my last one was a few years ago) in the Shadowrun universe, and I have 5 full length novels on my website ranging from about 70,000 words to over 450,000 words. I’ve been told that some of my stuff is as good as the published SR fiction, and it got me a gig working on actual Shadowrun material (both game materials and fiction, though I never snagged a novel gig, unfortunately, partly because when I was doing most of my writing, their novel line was on hold). I’m proud of my stuff (which is set in the game universe but includes all original characters) and I’m confident that if I was willing to pursue it hard enough, I have a good shot at getting a novel.
Why don’t I do it? Why don’t I try to write an original novel? Laziness, honestly. I’m terrible at selling myself. I don’t like doing all the little tasks that one would need to do in order to shop a novel around. I’ve actually got an idea for one that I think is pretty cool, set in an original universe and using versions of my characters that I used in my SR novels with all the SR bells and whistles filed off. Someday I might write it. But for now, the effort is just more than I want to make, since I have a good job and other stuff I’d rather be doing in my leisure time.
So instead, I write fanfic stories and bask in the kind words and emails that my readers send me. One time, somebody who hated one of my stories was even kind enough to write a multi-thousand word parody of it that cut right to its faults and made me laugh my ass off because it was so good. Never did find out who wrote it, though–I wanted to send him a “Well done!” 
Isn’t it fascinating that someone can dislike a thing so much that they spend all their time and energy on it like that?
I’ve done both. I’ve written over 100 fanfic pieces. I’ve also published one fantasy novel and a handful of short stories set in my own medieval alt-history world and am working on the second novel in what I hope will become a series.
The last time this subject came up, I said something to the effect that the difference for me is in the choices you make while writing. When you’re writing fanfiction, you’re (or at least I’m), doing variations on a theme. Looking at one canonical story plot point, I can come with a number of What-if scenarios as jump-offs to build my own story ideas on. And then I can write and post them all. When I’m writing my own story, I have to make one choice about where the story is going to go.
And, as Pepperlandgirl said, there is a nice, immediate gratification in writing and posting fanfic that you don’t get from writing professionally.
I write fanfiction and original fiction, with hopes that someday I might eventually finish a novel and sell it…maybe even the one I’m currently working on. So do lots of people. I know there are Rob Thurman fans here, guess how she got her start: Ghostbusters fanfiction. Several of the better known authors in my fandom (X-Files) are now published authors too…
I think there’s a lot to be learned from writing fanfics, and most any practice makes for stronger writing, so why not? I’ve personally learned a lot about pacing stories and creating effective scene breaks though writing fics, and I doubt there’s anyone out there who hasn’t learned anything. You should see the fics from an author I’ve beta’d for recently: the first few had dreadful mechanics, but she’s taken what I’ve been explaining to her as I correct errors to heart, and the latest one only needed a handful of errors fixed. So, she’s definitely improving through writing fics.