Jaxxy,
I don't know if this link provides any information that is new to you, but I'll let you look for yourself anyway:
http://www.chillingeffects.org/fanfic/faq.cgi#QID523
It talks about whether sexually explicit fiction has US First Amendment rights to free speech. The short answer seems to be... kinda.
Also, I've been doing more poking about... I don't know if anyone has already mentioned this in a previous post, but in 2001 a guy named Brian Dalton was convicted and jailed for writing about child pornography. He spent 2 years or so in jail before he won the rights to have a new trial. The conviction was thrown out of the Ohio court because the law only covered acts involving REAL children.
http://www.firstamendmentcenter.org/%5Cnews.aspx?id=12799
That does set a legal precedence, but one problem is that this guy wrote the stuff in his own personal journal, with no intention of distributing it. So would the precedence still apply?
This one will interest you the most, Jaxxy:
http://www.firstamendmentcenter.org/news.aspx?id=17458
This is about how a woman running a website that contained fictional graphic stories involving minors was indicted on obscenity charges. She was convicted and sentenced to 5 years probation and 6 months of house arrest. And her website was positively tiny in comparison.
To be quite honest, Jaxxy, if this woman wanted to take it further - and she was serious about it - then it sounds like she could indeed cause a LOT of trouble to come flying your way. I totally understand people saying "Don't give in!" but when it's your potential freedom at stake, you need to think VERY seriously about it.