The categories outlined in Barak's post describe the sorts of material that aren't allowed on LiveJournal -- either because it's prohibited by United States law, or because it's prohibited by our Terms of Service. To reiterate, though, we take a zero-tolerance stance on these sorts of material:
1. Material which violates United States law
Our servers are located in the United States, and so that means that LiveJournal is subject to United States law. This particular item in our policy covers content that inherently violates specific United States criminal statutes. (That is, the material itself is against the law.)
This includes threats of physical harm against the President or other executive officers, child pornography (photos or videos), or other material -- including drawings and text -- that explicitly depicts minors under the age of 18 (real or not) in a graphic sexual context. Or, in other words: Romeo and Juliet is okay. Teens talking about their experiences with sex is okay. Smut focused on a twelve year old is not okay.
These laws aren't unique to LiveJournal or even the Internet -- all media and publications in the United States are subject to them, and so we need to make sure that stuff on LJ doesn't violate these laws.
2. Material which encourages or advocates hate crimes, rape, or child abuse or pedophilia.
Stated differently, any material which indicates that these crimes are good or that they should be committed -- none of that is permitted. Effectively, you can't use LJ to promote these activities.
Again, though, we take things in context. If you're discussing the clinical diagnosis of pedophila, if you're discussing your experiences as a rape survivor, if you're discussing the actions that occurred in the Holocaust -- those are all fine. But content such as "Hitler killed millions of people, and someone should pick up where he left off" or "adults should be allowed to have sex with children" isn't permitted.
3. Material that asks for assistance in committing illegal activities that cause serious physical/economic harm to others.
Or, in other words, you can't use LiveJournal to plan, offer, or instruct others on how to commit serious illegal activities. The goal here isn't to prohibit every single illegal action. Rather, when we say "serious illegal activity", we're referring to activities that cause some sort of physical/economic harm to others.
Some of you were asking about things like speeding, gay marriage, jaywalking, purchase of sexual equipment, underage drinking, etc. None of those would be prohibited by this policy. But you can't post an entry asking for someone to help you beat someone up; you can't post entries asking if anyone knows how you can get around the anti-theft guards at an electronics store. That kind of thing.
We know there are grey areas and borderline cases, but there's no possible way we can make a list of what's acceptable versus what's not acceptable. (I've been reading Abuse complaints for three years, and someone comes up with something I've never seen before at least once a week.) When those cases come up, though, multiple people review them -- including members of our Abuse Prevention Team, LiveJournal and Six Apart staff, and our legal counsel. These sorts of decisions aren't made in a vacuum, nor are they made by just one person.
This should hopefully clarify most of the concerns that were raised regarding the specifics of our policies. As always, we'll be reading the comments here, but we can't guarantee that someone will be able to respond to every one.
CLARIFICATION: Not all content describing underage sexuality is in violation of our policies (or of United States law). Rather, using LJ to distribute "obscene" content (as defined by the Miller Test) is illegal. If it qualifies as obscene, and if it involves minors (people under the age of 18), then it's not allowed.
More clarifications are in the next post in this community.