My own sense so far is that Creative Commons is a spectacular project. It is interesting to note that it is not necessary or even likely that a work associated with Creative Commons will literally enter the public domain; the project is more complex and more flexible. Should we then ask whether the glass is half empty or half full? Creative Commons gives people an easy means—a computer-readable, searchable means—to assert what they desire with respect to content they create. This may result in more content being more clearly omitted from the public domain than clearly placed there, as candidates for Creative Commons licenses could be drawn from works that would otherwise be released entirely into the public domain, rather than works that would otherwise be copyrighted in the traditional way. Digital rights management systems could easily be placed on top of the machine-readable code, making the licenses self-enforcing. So you might even think of Creative Commons as converging with what the British Patent Office report called for: a greater understanding by people of the rights they have and can assert in the works that they create; an easy, simple, nonlawyerly way of expressing that desire; and, to the extent possible through machine execution, having it be so. One should note that this is a goal different—perhaps laudable, but different—from the goal of having as much material as possible enter into the public domain.
Another aspect of this discussion is important to note: the problem of derivative works is less a problem in relation to creative works than it is in software. In creating software, the purpose of using another's source code is to create a new code that does something else. In this sense, one directly “builds on the shoulders of giants” with software—something one does more conceptually than literally with creative work. An author does not literally have to incorporate another's poem into her own to have a successful or meaningful new work.
Finally, in the area of the scientific and technical data not subject, at least in the United States, to copyright protection, Creative Commons offers an opportunity to affirmatively and publicly catalogue the data, allowing the author to make clear the fact of his or her original production of them for attributive purposes. Scientific researchers thus can encourage maximum dissemination of their discoveries and methods, without sacrificing the fact of their own contributions to those discoveries.
What, then, is the real value of Creative Commons? First, it helps us to identify works intended for the public domain. Second, it helps people join the cultural melee. This is a battle over the description of rights, an assertion of copyright as an instrument, and not just an instrument for control. That part we understand quite well. Creative Commons helps to underscore the fact that a legitimate use of copyright is not simply to stop others from copying, but also to give permission—to imagine that something other than “All Rights Reserved” could be the phrase that follows one's assertion of copyright ownership.
Will Creative Commons work? That will depend on the value of the work committed to the public domain, or at least to public use, under the Creative Commons system. Exactly what sorts of authors and work it will attract, we have no idea. This is one of those ideas so new that one really has to make a leap of faith to see if it is going to work. And then, if it does work, it will seem obvious that it was a great idea whose time had long since come.