Update: There seems to be something on the move with GFDL / Creative Commons for Wikipedia contents. Look here to see what Jimbo Wales said: http://blog.jamendo.com/index.php/2007/12/01/breaking-news-wikipedia-switches-to-creative-commons/
just a few things...
Why not just use the Creative Commons? 
- Creative Commons did not exist when Wikipedia was created in early 2001. The Attributions-ShareAlike license is very similar in spirit to the GFDL, but not quite compatible with the present GFDL.
Why not switch to license XYZ? 
- Even if we wanted to, that's not really possible.
- Because contributors retain copyright to their submissions, it's not possible to unilaterally change the license, unless the Free Software Foundation consents to the change in a new version of the GFDL.
- Note, you could try dual licensing your stuff (see Guide to the CC dual-license) but that might not get very far if many other users do not follow suit.
What about invariant sections? Everyone says those are trouble. 
- Wikipedia doesn't accept invariant sections. While someone could create a derivative work from Wikipedia material and include invariant sections in that, the original Wikipedia version will remain unencumbered.
- The GFDL requires that derivative works list the "primary authors" of the original work on the title page, up to 5 if there are more.
- There have been some suggestions on how best to make it easy to deal with this requirement by automatically extracting a list of authors from page history, but this isn't fully realized yet.
Title page?? 
- The GFDL was originally meant for software documentation, such as manuals. For Wikipedia as a whole, the main page(s) can be considered as the title page. For extracting individual articles...?