I just realized something I should have a long time ago; Our use of the GNU FDL is completely copyleft. Read below;
:Permission is granted to copy, distribute :and/or modify this document under the :terms of the GNU Free Documentation :License, Version 1.2 or any later version :published by the Free Software Foundation; :with no Invariant Sections, no Front-Cover :Texts, and no Back-Cover Texts.
Note especially "with no Invariant Sections, no Front-Cover Texts, and no Back-Cover Texts." Hence, we only give permission to use our text if the 3rd part does /not/ add Invariant Sections, Front-Cover Texts, or Back-Cover Texts.
Therefore, for example, Britannica could never legally incorporate Wikipedia's content and add a Britannica-ad in an Invariant Section linked from every article. That way, every improvement they make to the Wikipedia content can be backported into Wikipedia. The cycle of positive-feedback continues.
This makes me feel much better about our use of the GNU FDL.
-- Daniel Mayer (aka mav)