um, let me see here. fan fiction.... hmmmm.
I saw Steph's answer on my friends page and have to agree with everything she said. It's a great way to "fix" shows, it let's people improve their writing ability while working with established characters and it's a wonderful way to meet new people. I also think it's a great way to relieve frustration about things in daily life because you can escape into the world either you or the show created and relax for a time.
Not to mention it's totally fun.