All,
We've chosen a license. It's CC-by-sa. (Technically, CC-by-sa version 3.0 unported.)
Our press release can be found here: http://en.citizendium.org/wiki/CZ:Citizendium_Press_Releases/Dec212007
And Larry's essay on why CC-by-sa is here: http://www.citizendium.org/czlicense.html
It's long, but I think it's quite a solid piece of argument.
So, what does this mean? If Wikipedia does choose to (in effect) relicense under CC-by-sa, as looks likely, our projects will be able to seamlessly share content.
I think this will be good for Citizendium, good for Wikipedia, and good for individual contributors split between the two projects.
Mike Johnson