While not commenting on the merit of the "how to get a girl" Wikibook, I'd just like to say, as a co-founder of Wikibooks, that I never intended Wikibooks to only have what would classically be seen as textbooks (although that was the focus).
Manuals, self-help guides, and even longer format reference books that are so popular in bookstores (such as a 200+ page biography about Napoleon) should, IMO, also be welcome. I also don't see how having those type of works on Wikibooks is in any way inconsistent with the foundation's goals.
The problem is that among the Wikibooks community there seems to be a lot of consensus in keeping only the academic textbooks and moving everything else to Wikicities: a book on Star Trek would probably be deleted as someone will say it is better suited to Memory Alpha, or a game guide on Gameinfo. A lot of folks in the Wikibooks community also like to adopt a version of Google's AdSense policies in trying to make the 'books more like the 'cities. This is one of the reasons why I've left the Wikibooks community (the other is the lack of something that combines wiki-editability with a relational database paradigm).
Also to be noticed is how community consensus is very difficult on Wikibooks: after all, why are we discussing what is and what is not appropriate on Wikibooks. The Wikibooks community has tried many ways to keep everything in order: [[WB:NP]], [[WB:CCO]], among others - it's just that none of them are flying (then again, there was a time when WB had no active admins, either...).
On the subject of [[WB:NP]], not a lot are agreeing to it because of limitations in the MediaWiki software itself: NP uses a hierarchy to organize book structure, but that leads to long pages and long links, and in many cases links are only within a book. Furthermore, a lot of users currently object to template and category naming conventions, as well as "book shortcut" names (say, C for [[Cookbook]]). Also, how a book is defined has come into dispute: some call [[Programming]] a book and [[Programming:C plus plus]] a chapter in a book, while others say [[Programming:C plus plus]] is a book and [[Programming]] a bookshelf (the debacle in which I was involved led contributors to [[Programming:Ada]] move the entire book to [[Ada programming]].
Then there's the debacle on what goes where - the material in [[Biography of Nikola Tesla]] was moved to WB as WP editors feel it didn't belong there, while it was deleted and undeleted over whether a biography was considered to be instructional material (or at least, belonging to WP rather than WB).
In short, Wikibooks has a really big problem of being vaguely defined, or defined in such a way that there are many interpretations of what to include in Wikibooks.