Harry Potter: Part 3 - Fanfiction, an Introduction

I'm not going to say much here, partly because I've just written two posts and I have a life to lead. But I do want to lay down some preliminary questions about Harry Potter-related fanfiction, which I'm going to be thinking about over the next few weeks/months, especially as I continue to read examples of it:

• Why do people write fanfiction? Is it to fill in gaps they've identified in the books, to explore issues that are not resolved, to alter the world to fit their preferences, to experiment with alternate possibilities? (I suspect all of these are true in some cases.)
• Are there common themes in the stories that receive the most critical attention? (I am measuring critical attention in terms of numbers of reviews on a site such as fanfiction.net or harrypotterfanfiction.com. The vast majority of these reviews tend to be laudatory, often emphatically so.)
• How are new romantic/sexual pairings presented, and how often are the characters kept IC (in character) or taken OOC (out of character) in order to present them?
• How are themes that would be considered incompatible with the genre of children's literature (especially deviant sexual behaviour) presented?
• Who writes fanfiction? Male or female? What kind of age? (In the media, the genre is largely presented as a realm dominated by teenage girls, but this cannot be exclusively true.)
• How much of themselves do fanfiction writers tend to reveal about themselves, and how often does this relate to how they write or what they write about?
• How often is the loose generic allocation of 'fantasy' to the Harry Potter books manipulated or destroyed?
  

I'm sure other questions will appear during the course of this series, but for now we'll leave it there.