http://thunar.xfce.org/news.html <snip> dependency of the thunar-vfs library on GConf for thumbnailers is gone and the thumbnailers are now loaded from an automatically generated thumbnailers cache </snip> Thanks to Andrey Melentyev for reporting.
Maybe but: Thunar-0.8.0 # less configure.in ... XDT_CHECK_OPTIONAL_PACKAGE([GCONF], [gconf-2.0], [2.4.0], [gnome-thumbnailers], [GNOME thumbnailer support]) ... Additionaly when You don't have GConf in system: Thunar-0.8.0 # ./configure --enable-gnome-thumbnailers ... checking for optional package gconf-2.0 >= 2.4.0... not found ... * GNOME Thumbnailers: no ... So it is needed or not? Maybe it is only about thunar-vfs library, not thunar as a whole application.
INVALID, get this fixed upstream if you don't want gconf.