I like the Creative Commons By Attribution
license - it's more free, letting people mix the content more easily and use it how they want, even mixing it with non-free content - as long as they give attribution.
The challenge is, if we decide to switch Appropedia to this license, much of our content will have to be clearly marked as being under a different license. (I'm thinking a template top and bottom, and some kind of box for content on pages where the content is from mixed licenses - we'll need to use a bot to put the notices on every page, to start with.)
We'll want to contact as many editors as possible and ask them to release all their past contributions under the new less restrictive license, and begin a process of identifying which old content can have the "GFDL" mark removed, to bring it over to the new license.
I believe it will be worth the pain, and we're starting to discuss it within Appropedia now.
See Which free license should you use?