I had been putting it off recently because it was "good enough" and I had other items on my todo list with higher precidence. However recently I've spent a few hours working on my MediaWiki Book Designer extension, and I'm starting to make some real progress with it.
As a bit of history, I started working on the designer when I was an active Wikibookian. It was born from my experience helping new users to get started writing books at Wikibooks, which ended up being unnecessarily complicated. The MediaWiki software is primarily developed and targeted for use with Wikipedia, not Wikibooks after all.
A graphical book outlining tool was one of the major deliverables requested from my contract with the Wittie group, and I was already mostly finished working on the first version of it on Wikibooks. As part of my work on the Wittie project, I slimmed the designer tool down to an easy-to-use subset of features, made a few improvements to the UI, and even wrote up a proper PHP backend to it that I didn't have access to do at Wikibooks.
Not too long ago I pushed my work to Github, where it sat without much fanfare.
Late last week I got a message on github from the first confirmed independent user of my extension. Also this week begins the spring semester and the Wittie group have been asking for a few improvements to the extension so they can begin creating new books for the new semester. These things together have spurred me on to begin a new round of hacking. Specifically I'm working on UI improvements, decreasing memory consumption, i18n compliance, and a series of other small fixes and feature additions.
I've also been spurred on to setup a proper testing environment on my personal laptop. Luckily this is quite easy in Ubuntu: install the mediawiki package, enable mediawiki in the Apache config file and restart Apache, setup the wiki, checkout the BookDesigner gadget into the extensions folder, and add a single require_once() directive in the wiki PHP code. Probably took me less than 5 minutes total.
It's too bad I'm not an active Wikibookian anymore, this tool would really be making my work there much easier. When it gets a little bit more mature I think it will be a real boon for wiki-based book writers. Still plenty of work to do before we reach that point, however.