I have only give about half a dozen entries in my game book written up, because in the last week I have been distracted by another writing project.
I decided to enter a "one page dungeon" competition hosted on the Role Playing Geek web site. During the creation process of a dungeon, I actually not only invented a dungeon but also the bare bones of a whole role playing game. That sounds like a lot of work, but wasn't really. The one page dungeon itself was knocked up within an evening...and so this wasn't really the distraction.
What the distraction was, is that the bare bones RPG I came up during that process deserved to be fleshed out into a real full length game. This is where I've been spending my writing time.
It's interesting to note that the one page dungeon competition is not a money making project, but that short diversion has set me off on this RPG project which will be a money maker.
Anything "Cthulhu" or "Lovecraft" is extremely popular at the moment so the RPG I'm writing is themed that way. A completely opposite direction from the original one page dungeon.
I think that this proves that taking the occasional diversion can really inspire the muse. As a bonus this project is shorter than the game book project so will be finished quickly.