I've been thinking about writing some smut -- I have some good ideas that I obviously would rather not bring intro fruition through more... ehm, "mainstream" means .x. However, I'm not certain: What are this website's stipulations on posting stories? Is it allowed? If not, where would you guys recommend I do it?

There's no ruling against it. I had a thread once where I wrote about futa and took some request.

I say go for it, just be aware you're gonna get people that disagree with it and try to start an argument. I like the idea though :)

Are the story concepts related to Rule 34 or work with wholly original characters?

you could always post your work offsite and link to it here instead of copypasting word walls