Don't know too much about the history of this bug.  I just did a clean install of kubuntu 9.10 and i'm getting similar messages.  Though it doesn't appear to be fatal, seeing something that is obviously wrong repeating itself all the time is a bit disturbing, especially since for all I know, it is affecting something in system performance.  Maybe this is a plasma-desktop bug?  It seems to be the same as the one documented above.  Anyhow, I get stuff like:

Nov 10 17:04:01 cleverbox dbus-daemon: Rejected send message, 1 matched rules; type="method_call", sender=":1.20" (uid=1000 pid=1675 comm="kdeinit4: plasma-desktop [kdeinit]") interface="org.freedesktop.DBus.Introspectable" member="Introspect" error name="(unset)" requested_reply=0 destination=":1.21" (uid=1000 pid=1677 comm="kdeinit4: kio_trash [kdeinit] trash local:/tmp/kso"))
Nov 10 17:04:01 cleverbox dbus-daemon: Rejected send message, 1 matched rules; type="method_call", sender=":1.20" (uid=1000 pid=1675 comm="kdeinit4: plasma-desktop [kdeinit]") interface="org.freedesktop.DBus.Introspectable" member="Introspect" error name="(unset)" requested_reply=0 destination=":1.6" (uid=0 pid=1039 comm="/usr/sbin/console-kit-daemon))
Nov 10 17:04:01 cleverbox dbus-daemon: Rejected send message, 1 matched rules; type="method_call", sender=":1.20" (uid=1000 pid=1675 comm="kdeinit4: plasma-desktop [kdeinit]") interface="org.freedesktop.DBus.Introspectable" member="Introspect" error name="(unset)" requested_reply=0 destination=":1.19" (uid=1000 pid=1675 comm="kdeinit4: plasma-desktop [kdeinit]"))
Nov 10 17:04:01 cleverbox dbus-daemon: Rejected send message, 1 matched rules; type="method_call", sender=":1.20" (uid=1000 pid=1675 comm="kdeinit4: plasma-desktop [kdeinit]") interface="org.freedesktop.DBus.Introspectable" member="Introspect" error name="(unset)" requested_reply=0 destination=":1.5" (uid=0 pid=1041 comm="NetworkManager))
Nov 10 17:04:01 cleverbox dbus-daemon: Rejected send message, 1 matched rules; type="method_call", sender=":1.20" (uid=1000 pid=1675 comm="kdeinit4: plasma-desktop [kdeinit]") interface="org.freedesktop.DBus.Introspectable" member="Introspect" error name="(unset)" requested_reply=0 destination=":1.16" (uid=1000 pid=1628 comm="kdeinit4: kded4 [kdeinit]))
Nov 10 17:04:01 cleverbox dbus-daemon: Rejected send message, 1 matched rules; type="method_call", sender=":1.20" (uid=1000 pid=1675 comm="kdeinit4: plasma-desktop [kdeinit]") interface="org.freedesktop.DBus.Introspectable" member="Introspect" error name="(unset)" requested_reply=0 destination=":1.15" (uid=0 pid=1509 comm="-:0))
Nov 10 17:04:01 cleverbox dbus-daemon: Rejected send message, 1 matched rules; type="method_call", sender=":1.20" (uid=1000 pid=1675 comm="kdeinit4: plasma-desktop [kdeinit]") interface="org.freedesktop.DBus.Introspectable" member="Introspect" error name="(unset)" requested_reply=0 destination=":1.12" (uid=0 pid=1209 comm="/usr/lib/hal/hald-addon-storage))
Nov 10 17:04:01 cleverbox dbus-daemon: Rejected send message, 2 matched rules; type="method_call", sender=":1.20" (uid=1000 pid=1675 comm="kdeinit4: plasma-desktop [kdeinit]") interface="org.freedesktop.DBus.Introspectable" member="Introspect" error name="(unset)" requested_reply=0 destination=":1.11" (uid=0 pid=1127 comm="/sbin/wpa_supplicant))
Nov 10 17:04:01 cleverbox dbus-daemon: Rejected send message, 1 matched rules; type="method_call", sender=":1.20" (uid=1000 pid=1675 comm="kdeinit4: plasma-desktop [kdeinit]") interface="org.freedesktop.DBus.Introspectable" member="Introspect" error name="(unset)" requested_reply=0 destination=":1.20" (uid=1000 pid=1675 comm="kdeinit4: plasma-desktop [kdeinit]"))
Nov 10 17:04:02 cleverbox dbus-daemon: Rejected send message, 1 matched rules; type="method_call", sender=":1.20" (uid=1000 pid=1675 comm="kdeinit4: plasma-desktop [kdeinit]") interface="org.freedesktop.DBus.Introspectable" member="Introspect" error name="(unset)" requested_reply=0 destination=":1.22" (uid=1000 pid=1697 comm="kdeinit4: kmixctrl [kdeinit] --restore"))
Nov 10 17:04:03 cleverbox dbus-daemon: Rejected send message, 1 matched rules; type="method_call", sender=":1.20" (uid=1000 pid=1675 comm="kdeinit4: plasma-desktop [kdeinit]") interface="org.freedesktop.DBus.Introspectable" member="Introspect" error name="(unset)" requested_reply=0 destination=":1.23" (uid=1000 pid=1701 comm="kdeinit4: krunner [kdeinit]"))
Nov 10 17:04:04 cleverbox dbus-daemon: Rejected send message, 1 matched rules; type="method_call", sender=":1.20" (uid=1000 pid=1675 comm="kdeinit4: plasma-desktop [kdeinit]") interface="org.freedesktop.DBus.Introspectable" member="Introspect" error name="(unset)" requested_reply=0 destination=":1.24" (uid=1000 pid=1709 comm="kdeinit4: kio_trash [kdeinit] trash local:/tmp/kso"))
Nov 10 17:04:07 cleverbox dbus-daemon: Rejected send message, 1 matched rules; type="method_call", sender=":1.20" (uid=1000 pid=1675 comm="kdeinit4: plasma-desktop [kdeinit]") interface="org.freedesktop.DBus.Introspectable" member="Introspect" error name="(unset)" requested_reply=0 destination=":1.25" (uid=1000 pid=1718 comm="kdeinit4: kmix [kdeinit] -session 10140dec7e500012"))
Nov 10 17:04:11 cleverbox dbus-daemon: Rejected send message, 1 matched rules; type="method_call", sender=":1.20" (uid=1000 pid=1675 comm="kdeinit4: plasma-desktop [kdeinit]") interface="org.freedesktop.DBus.Introspectable" member="Introspect" error name="(unset)" requested_reply=0 destination=":1.27" (uid=1000 pid=1732 comm="/usr/bin/knetworkmanager))
Nov 10 17:04:52 cleverbox sudo:    micha : TTY=pts/1 ; PWD=/home/micha ; USER=root ; COMMAND=/usr/bin/apt-get install digikam gimp
Nov 10 17:05:29 cleverbox dbus-daemon: Rejected send message, 1 matched rules; type="method_call", sender=":1.20" (uid=1000 pid=1675 comm="kdeinit4: plasma-desktop [kdeinit]") interface="org.freedesktop.DBus.Introspectable" member="Introspect" error name="(unset)" requested_reply=0 destination=":1.29" (uid=1000 pid=1828 comm="/usr/lib/firefox-3.5.6pre/firefox))
Nov 10 17:05:31 cleverbox dbus-daemon: Rejected send message, 1 matched rules; type="method_call", sender=":1.20" (uid=1000 pid=1675 comm="kdeinit4: plasma-desktop [kdeinit]") interface="org.freedesktop.DBus.Introspectable" member="Introspect" error name="(unset)" requested_reply=0 destination=":1.30" (uid=1000 pid=1838 comm="/usr/lib/libgconf2-4/gconfd-2))

It would certainly be nice to see a fix for this if possible.