This is a follow up of http://bugs.archlinux.org/index.php?do=details&id=1372 (I can't reopen the task). There's a (major) but in the sugestion there, refering to XDG_DATA_HOME.

The full documentation regarding XDG variables can be found @ http://freedesktop.org/Standards/basedir-spec (v0.6)
I also found http://kde.ground.cz/tiki-pagehistory?page=Environment+Variables

After going through those 2 pages, I came to the conclusion that a profile.d/xorg.sh should look something like:
<code>
export XDG_DATA_HOME=$HOME/.local/share
export XDG_CONFIG_HOME=$HOME/.config
export XDG_CACHE_HOME=$HOME/.cache

if [ ! -z $XDG_DATA_DIRS ]; then
export XDG_DATA_DIRS=/usr/share
else
export XDG_DATA_DIRS=/usr/share:$XDG_DATA_DIRS
fi

if [ ! -z $XDG_CONFIG_DIRS ]; then
export XDG_CONFIG_DIRS=/etc/xdg
else
export XDG_CONFIG_DIRS=/etc/xdg:$XDG_DATA_DIRS
fi
</code>
Make sure /etc/xdg exists and with proper read rights.

IMO, the XDG specs should be checked every time a new xorg package is rebuilt.