Back in 2003, the first year the forums existed and when I was a baby WriMo, someone started a female masturbation thread asking exactly that. It was in fact for their novel. Then in 2005 (I think--the years are starting to run together now), someone started it for kicks (OMGIFOUNDIT) because no one had started it yet. The thread itself is tame, but then WriMos started to go after the people in the thread, especially as some of them were quite well-known for producing what I thought was hilarity around the forums. Unfortunately, I can't remember where the actual attacking happened at the moment, but it's scattered throughout the forums and not concentrated anywhere. Woe.

Either way, there's now a no sexual content clause in the terms of service (or is it codes of conduct?) now.