Comment 12 for bug 56426

"Ubuntu is supposed to be for everyone and many people wouldn't be able to figure this out."

If you can't figure this out, you oughtn't be fiddling around with the SysV init scripts. They're not for everyone. Things should "just work", without needing to mess with the initscripts. Once you do, you accept the responsibility to figure it out.

There's a toggle in GNOME: "System->Administration->Networking->General->Automatic service discovery" It makes the change in /etc/default/avahi-daemon. When someone decides to turn on avahi-daemon with a SysV symlink, that toggle will stop working.

(The many packages whose daemons can be disabled via debconf (which usually does the same thing) will have the same problem.)

If there's no way to turn that avahi thing on in $DESKTOP that's a bug. That avahi silently stopped working on upgrade, is a bug (that pref is hard to find!).

This is NOTABUG.

"As for precedents, a quick poke around in my /etc/init.d turns up no other examples of conditional startup installed at the moment."

You almost certainly do. You would have had better luck looking in /etc/default:

apache2
apt-cacher
avahi-dnsconfd
bittorrent
bootlogd (initscripts package)
dbus (and dbus-1)
ddclient
fetchmail
hal
hplip
mdadm
mldonkey-server
nfs-common (toggles for a number of daemons with a single initscript)
portmap
prelink
rscsi (refuses to run if the file in /etc/defaults is missing)
rsync
samba
smartmontools
spamassassin
watchdog

All of those packages (on my system) have the same sort of toggle in /etc/defaults (that affects the init.d script) -- many of them have a file in /etc/defaults for only that purpose.

This is a Debian "standard", just like the alternatives system, update-grub, update-mime, and all their friends.