On Tuesday, the Supreme Court heard oral arguments on Humanitarian Law Project v. Holder, a case that challenges the constitutionality of anti-terror laws (such as in the PATRIOT ACT) that makes it a crime to "provide material support" to terrorist organizations. The problem with the law is that it's quite broad; "material support" could mean a whole slew of things, from providing personnel to training to attorneys writing amicus briefs in their defense.
Of course, as Glenn Greenwald notes, so much of what is potentially a crime should be superceded by 1st Amendment rights. The New York Times has an interesting article on point here, as is this Yahoo! article.
Now, just to mix things up a little more: how attenuated does the support need to be? How much knowledge is there, or is it strict liability? What is a "terrorist organization?"
So many questions...