The most common questions I've received about the book are: "does it cover Heroku?" and "does it cover Google AppEngine?" I've chosen not to provide detailed coverage of these platforms in the book, but they are still excellent choices for JRuby deployment. As a result, I hope to post some tutorials of how to use them on this blog.
I'll also be posting updates on new platforms, and some less mainstream server technologies that can be used for deploying JRuby.
Stay tuned for more!