DocBook XSL: The Complete Guide – 4th Edition, Chapter 1. Introduction, Online resources for finding solutions to problems (the paper book and the online version as well) says, that the IRC channel of DocBook would be at irc://irc.openprojects.net#docbook, but it actually is at irc://irc.freenode.net#docbook.
http://www.docbook.org/help had the right information.
This is not on their Errata yet, and I told webmaster(AT)sagehill.net about this problem in the meantime. I only wondered for a very, very short time, whether anybody will ever come back to me.
Bob Stayton (himself) answered at 2010-07-06 22:12:18 (my time at Berlin, ie. only an hour or so later):
Apparently it changed since that was written.
I’ll put the new address in the next edition and add to the Errata.
Thanks for the report.
As I said, I will update this here, once I will notice their update.