This bug has been plagueing me and a lot of others for some time. As I mentioned in Hardy Heron Countdown, below,
the desktop fails to load properly every nine boots or so. It’s usually though not always accompanied by this bug notice:

click on image to enlarge

I got fed-up putting up with it (especially as while it’s usually ok after a restart, sometimes I’m forced to take out power, including battery, before it restarts properly), so I went hunting the bug.
It’s described at http://bugzilla.gnome.org

gnome-session does not wait long enough for dbus-daemon to start

Apparently, this is what happens

dbus-daemon starts, then dies on SIGPIPE. This results in all dbus-dependent
desktop components to either die (SIGABRT) or misbehave.

Expected results:
dbus-daemon should continue to run for the life of the GNOME session.

Does this happen every time?
No, but in GNOME 2.17, it is much more likely to happen.

As the version of Gnome which comes with Ubuntu Hardy Heron is 2.22, let’s hope that this particular nuisance is gone for good.