After hearing some IRC chit chat, I ran across this "adult only" Harry Potter fan fiction site. Unfortunately you have to register an account just to even peak at the rather ... interesting content.
Hello, and welcome to the Restricted Section. In the wake of fanfiction.net's decision to remove all NC-17 content, a group of Harry Potter fanfiction authors decided to open a new archive devoted to adult Potterfic. This means that this site is strictly for people over the age of 18. If you are underage, perhaps the The Leaky Cauldron or FictionAlley would be more to your liking.
Harry Potter Porn / Fan Fiction - RestrictedSection.org