It is my understanding that copyright to everything in Wikipedia belongs to the contributors, who are releasing it under the GNU FDL. Wikipedia has a copyright on the _compilation_, which means something very specific under copyright law, and we release the _compilation_ under the GNU FDL.

The downside of this arrangement is that if someone takes portions of wikipedia and does something counter to the GNU FDL, we are not in a position to defend it. That's not a good thing. I suppose that if that were to happen, and if I were to be in the mood to defend it, we could ask contributors to those specific sections to _at that time_ sell us their copyright for a dollar, so that we could pursue the infringers in court.

The upside of this arrangment, if there is one, is that even Wikipedia can't make the content proprietary.

Another potential downside to this arrangement, and I'm not sure how important this one is, is that many overly cautious potential licensees of the content will hesitate to license it absent a single unified ownership. For example, Yahoo might not want to use Wikipedia content as the basic for Encyclopedia Yahoo, if they were to create such a thing, out of concern about there not being a single licensing authority.

--Jimbo