Text-based erotic stories in general are mostly the province of girls. Yaoi stories are a subset of that, still largely by and for women. (Of course there's also manga and whatnot; I have less explanation for that.)
The link Khafra gave me the impression that Yaoi was often graphical too (compared to anime or manga). Does the same trend apply to those works? (Or, perhaps, are the wikipedia authors just biassed towards graphical media?)
Update: This post has also been superseded - new comments belong in the latest thread.
The second thread has now also exceeded 500 comments, so after 42 chapters of MoR it's time for a new thread.
From the first thread: