Incompatibility between latest passwd file and dbus
Last week I installed a filesystem update that included a new passwd file. It lacked the avahi and dbus users, and contained a new user called uidd. After adding myself (natch!), I installed it. The next boot was a complete mess because dbus expects the avahi and dbus users to be available. The avahi user is referenced in avahi's dbus configuration file, and dbus is the user that the system-wide dbus daemon actually runs under.
I restored the old passwd file and everything was OK for a while. Today I did another update and had trouble upgrading util-linux because it needs that new user "uidd". I had to add that user to the file by hand.
I've seen nothing on the Arch Forum about anyone else having these problems and I've found nothing about it on the Web. My fixes are kludges and I'd like a more elegant and permanent way of sorting this out.