Or in a better phrasing, possibly my final excuse to quit using Gnome entirely.

I have finished - almost - setting up an Arch install, and I'm trying to sort out the WM and DE I want.
I keep Openbox around for various reasons, it's installed fine, and I can (manually) launch it.
Gnome, however is being a pain. On installing, it gives a whole load of GConf errors, most of which look something like this:
For almost any package that gets pulled in with 'pacman -S gnome gnome-extra'
This seems to have had the knock-on effect that when I add GDM to the daemons in /etc/rc.conf, GDM launches, but then displays a little notification saying that gnome-power-manager wasn't installed correctly (Which aside from above GConf error happening to it too, it was) and then does nothing, and allows for nothing but moving a little black cursor around a grey background.

So far I've disabled GDM from launching, and tried running an update and reinstalling gnome and gnome-extra to no avail.
This is probably the last main problem I'm having that's stopping me declaring Arch sucessfully installed and on it's way to stealing my attention from Slackware and Fedora.
And if it doesn't work, then maybe it's about time I dumped it for KDE, and tried to figure out what alternatives to some gnome-specific stuff I have are.

This seems to be similar to what you're suffering. Possible solution in the bug report.

The solution... sort of worked.
GDM launches without any complaints now, but instead it just gives me a bright green screen, that reacts only to the power button being pressed.
It's progress, I guess.

Have you tried Slim starlion?

Slim works great in my arch/slack/debian/ubuntu installs
autologin for root too

Thanks for the idea, but I prefer using GDM. I don't use autologin, especially not for root (Which I don't even login through su now I've setup sudo).
GDM provides what I'm after a lot easier for me.