I feel really bad that, all of the times I've mentioned fanfiction in the past, I've referred to it as something that takes time away from "real writing". Just because the original work on which your story is based was written by someone else, a good fanfiction still begins with an unique idea.
Maybe it's just me, but I often see people describe fanfiction writers as something "less"**. The main purpose of a fanfiction (and sorry for using the word so many times--I can't seem to think of a decent pronoun) is to entertain. Like all stories should. Writers = entertainers = story tellers. It's the same thing, no matter what your genre or starting point is.
Some of the most creative scenes and characters I've read have been in fanfictions. That's why I love sites like fanfiction.net that provide a place to publish your stories. Writing fanfiction isn't just a fun hobby to exercise your writing muscles--you can get feedback and critiques on your writing, plus make a few friends who are interested in the same things as you. Okay, sorry, way to sound like a greeting card. But think about it--let's say you really hate the ending of a book (for example, the epilogue of Harry Potter and the Deathly Hallows). By writing a fanfiction, not only can you write as some of your all time favorite characters, you can control the outcomes.
The one good thing about fanfiction not being considered as important or artistic by some people as, say, writing a novel, is that you don't have to take yourself too seriously. Come up with a username, write a story, and put your work out there. You can have fun with random scenarios, one-shots, and the most ridiculous dialogue (the term "Merlin's magic panties" came up the other day). And if you want to improve your writing style, why not work at it while doing something fun?
In short, yes, I write a fanfiction. No, I'm not a crazy fan-girl, and I don't spend all my time on it. In the future, I want to be writing novels--but writing fanfiction is a really fun way that I can connect to people who like the same books as me, and apparently like my writing. Huh. How about that.
**I'm sorry, I really don't me to generalize, but bring up "fanfiction" in a conversation has always made me feel weird and kind of inadequate compared to those people--you know, the ones who read Tolstoy when they were six, and are working on their latest work of speculative fiction.
I want to have fun with writing. I believe that I like having fun.