I run Fluxbox as my primary window manager, and use gnome-settings-daemon to keep gnome apps happy and GTK-informed. Thus far, all has gone well. However, OpenOffice.org does something very funky to determine whether one is using KDE or GTK, finds neither on my system, and drops back to the horribly ugly interface of 1997.
I haven't figured out how to fix this yet, but running gnome-session sets up something which convinces OpenOffice to use the GTK theme. It doesn't appear to be an environment variable, because I can set my environment identically under gnome and fluxbox, with no difference in OO behavior. My guess is there's some sort of socket or temporary file set by gnome-session, but it's all a mystery and the source is obfuscated. If anyone knows of a way to force OpenOffice 2.0 to use GTK, I'd be interested to hear about it.