As you know, I am writing on a book about JRuby on Rails. A few minutes ago I finished the first draft of chapter 14. That means that there are just 3 chapters and 3 appendixes left to write (chapter 1, 2 and 15). So the writing is going very well, but it's taking a heavy toll on me personally. I seriously don't recommend writing a book like this in your spare time, while at the same time switching employer, moving abroad and try to be a core developer in an open source project which is getting lots of attention.
So, in summary: it's going well, it still looks like it will be out in October, and I'm deadly tired.