The Wikimedia Foundation has started a vote to enable a migration from GFDL licensing to dual-licensing GFDL and CC-BY-SA-3.0. All Wikibookians (in fact, all Wikimedians) are encouraged to vote on this issue, and it's my personal hope that they all vote YES! Here is the voting page. You must have at least 25 edits before you will be allowed to vote.
Dual licensing GFDL and CC-BY-SA-3.0 will keep our material compatible with all the GFDL stuff still, but will also open compatibility to other websites and organizations that are CC-BY-SA-3.0 only. A large number of organizations, especially open-education groups, use CC-BY-SA licenses for their content, and previously Wikibooks was not compatible with these. Now, if the vote is passed, we will be and licensing will no longer be a significant barrier to the free use of quality educational materials.
It is my personal opinion that this initiative will be immensely beneficial to the Wikibooks project, with no significant downsides. If people would like to explore other opinions, get in contact with me and I will be happy to send you links to other information that you can use to make a decision.