I recently dist-upgraded to this and for all the time since I've been trying to log in to GNOME. This is with GDM enabled under dpkg-reconfigure gdm.

It will get into the themed greeter and log in, but stops on Metacity and sits at two white gnome-panels in front of a black screen. Those panels kill themselves over and over ad nauseam and I have to Ctrl-Alt-Backspace to get out of this.

Is this a problem with the GNOME boot-up sequence, or just the usual invasiveness of KDE at work? (I use that for pretty much everything nowadays)

Lemme know.

dist-upgrade from what? have you tried a
apt-get update
apt-get upgrade
apt-get dist-upgrade
again to make sure everything is as it should be.