It seems that Erik has chimed in on this point with a remarkably good set of comments on the Foundation-l mailing list (I believe, in reply to Kat's announcement, which I previously blogged about here).
I especially liked "CreativeCommons is about giving choices to authors within a legal framework. Wikimedia is about building free culture." This is something close to what I was getting at in this post, but, uncharacteristically, Erik (who is quite well known for being prolix) managed to put it far more succinctly than I did. Good show, Erik.
This really helps to focus the problem that Wikimedia (and a lot of other free content creators) faces: Either use the GFDL, which is good at protecting free content but is a cranky and difficult to use license, or use CC-BY-SA, which is much easier to use but does a far poorer job of protecting the freedom of the content under it. On top of that, people so readily confuse CC-BY-SA with the other CC licenses -- most of which are not "free content" licenses, but merely "free redistributions" licenses. I'd really love to see either the FSF come up with a less prickly version of the GFDL, or Creative Commons produce an entirely new license (or set of licenses) that really are free content licenses. Or both.