Binary package hint: gnome-session
The problem is happening on my desktop with a high frequency but is not 100% reproducible. It usually happens on the first login after booting the system and can be fixed with a re-login.
The gnome theme simply fails to get applied, I get a working system but with a stock GTK theme.
DistroRelease: Ubuntu 10.04
Package: gnome-session 2.30.0-0ubuntu1
ProcVersionSignature: Ubuntu 2.6.32-21.32-generic 188.8.131.52+drm33.2
Uname: Linux 2.6.32-21-generic x86_64
Date: Mon May 3 09:47:13 2010
InstallationMedia: Ubuntu 9.10 "Karmic Koala" - Release amd64 (20091027)