Protecting Philosophical Ideas with Copyright?

I have opened a discussion on this subject at my law school blog in response to an inquiry from a philosophy graduate student.  One of my law colleagues, an expert on copyright, comments, and I am hoping other legal experts will weigh in.  Issues about the misappropriation of someone else's philosophical work or ideas often come up in informal conversation; faculty and students may find the discussion of the legal protections available of some value.