There was a Supreme Court case about this in the '60's regarding the councelling of men in ways to avoid the draft.

The Court ruled that general and non-specific writing and speech regarding the ins and outs of a criminal activity are not in and of themselves illegal, and consist of protected free speech.

The line is crossed when you actively participate in a crime by telling a person how and what to do in a specific instance.

Obviously the fine line is a gray area and depends on how a jury would interpret the intentions behind your activities.

(still not a lawyer)

that, like mrfisher says, you do not cross the line from speech to facilitating.  For example, you can probably write that there are web sites containing information on how to make a b***b (Patriot Act filter applied by author), but if you list the sites, you are arguably crossing a line.

This would be a very difficult case for any prosecutor to bring, so the more salacious the nature of the subject matter, the easier the case to bring.  You will probably not get popped for writing a hobby how-to, but if you went into tax evasion or b$$b making, you could.