Make sure you are running dbus.  I do this in .xsession:

  dbus-launch --exit-with-session gnome-session

I think it's a bug that you have to do this but apparently you do.

Also, on my -current dual processor machine, sometimes not all of gnome
starts on login, and 'pkill gnome-session' and logging in again always
makes it work.  On my netbsd-4 single processor machine, I have had no
such issues.