There's an ongoing enormous thread on the gtk-devel list (Is GTK+ a cross-platform toolkit ?). The gist is that there is some promising forward movement on the win32 front, with the current focus on improving the build system so that more people become capable of actually testing Glib/Gtk in a timely manner. The most active developer seems to be doing his work here: http://www.tarnyko.net/repo/gtk3_build_system/