Something significant has happened in the world of free licensing, Lessig has the details and a video. Apparently, an important step has been made towards interoperability between the license controlling Wikipedia articles (the GFDL v.1.2), and the CC license by-share-alike. (See also this post on the Creative Commons website).
The vision of all free licenses cannot be achieved when the legal landscape is too complicated. A lack of “interoperability” between different families of licenses is a symptom of complexity that flies in the face of the desired simplicity. That’s why interoperability is so important. In fact, the possible marriage (or fusion, if you like) between the GFDL and the CC-by-sa licenses should be a happy one. Both adhere to the same key principles of freedom while giving due credit to your source and passing along your new work under the same (free) conditions you have obtained and used the work of others. Interoperability means that in the future, people should be allowed to release content currently controlled by the GFDL under the CC license without violating the GFDL. A resulting shift of Wikipedia content to the CC license can enhance uniformity and the benefits from free licensing in general. I assume we'll hear some more details about this contemplated move soon.