I may be wrong but the legal standard being used is based on the Miller case. This case stands for the proposition that local community standards determines whether a) material appeals to "prurient interest" in sex [whatever the fuck that means...the US Supreme Court recently came up with more "specific" language--"morbid fascination" with sex... yeah, real clear!] b) the material has no serious literary, artistic, political, or social value.
Bottom line: depending on where you live, you may get fucked. The local community standard in a suburbian Arizona or Colorado neighborhood is different from that in Alabama which is different from San Francisco. However, since the Internet is everywhere and nowhere at the same time, jurisdiction issues are still up in the air.
What's troubling is a recent spate of international cases saying that local law applies to the Internet. Let's just hope this does not continue or our industry will become toast.
