From Steve's LJ, he said he was supposed to be half way through the book by October 2006 and there are a couple notes about him working on it, but nothing really about progress. However, a couple years later, Sharon posted this
http://rolanni.livejournal.com/482922.html . Very unoptimistic from that post. Some notes from Steve after the project fell through but before Sharon's post sounded like maybe there was a possibility that they might go back. I just hope Steve is right and the possibility of a book isn't really dead.