Yeah, I realize it's a slight tangent. I guess I consider automount a prerequisite for autorun, and I don't want either one to happen.
But thanks to your explanation about what Nautilus is doing, I was able to find the right gconf keys to flip in gconf-editor:
/apps/nautilus/preferences/media_automount
/apps/nautilus/preferences/media_automount_open
/apps/nautilus/preferences/media_autorun_never
Now I just wish I could keep Nautilus from even being triggered at all when media is inserted, unless I'm actually running GNOME.