I've seen an increasing demand for this, so... I've just made a public copy of JGC's excellent guidelines for Gnome packages here: http://wiki.archlinux.org/index.php/Gnome_package_guidelines This applies not only to Gnome packages but also to Xfce and some pure Gtk packages as well (not sure about KDE/Qt packages) - basically anything that use gconf, .desktop, hicolor icon theme etc. and is intended for usage in a desktop environment. (e.g. there's no need for Sauerbraten to use desktop-file-utils *just* because it includes .desktop file (it can be run a server only)).
There is a collector bugreport for this: http://bugs.archlinux.org/task/9217