Here's an interesting one. Everything was fine last night, did an update, shut down.

Started up this morning, GDM loads, log in -> back to GDM. Hmm.
Console, service stop GDM, service start LightDM. LightDM doesn't load (similar to missing or unbuilt kernel module for fglrx).
Reinstall fglrx, same thing.
Remove xorg.conf to load the OSS driver. Same thing. This is getting weird.

Console, login, startx:
xinit: connection to X server lost.

Server terminated successfully (0). Closing log file.

So, um, X is loading then quitting? Looking at the last update history:

Upgraded the following packages:
at-spi2-core (2.6.0-0ubuntu1) to 2.7.1-1
ca-certificates (20120623) to 20121105
coreutils (8.13-3.2ubuntu3) to 8.13-3.2ubuntu4
debhelper (9.20120608ubuntu1) to 9.20120909ubuntu1
dh-modaliases (1:0.2.71ubuntu2) to 1:0.2.72
gir1.2-atspi-2.0 (2.6.0-0ubuntu1) to 2.7.1-1
gir1.2-cogl-1.0 (1.10.4-0ubuntu1) to 1.12.0-1
gir1.2-coglpango-1.0 (1.10.4-0ubuntu1) to 1.12.0-1
libasound2-plugins (1.0.25-2ubuntu2) to 1.0.25-2ubuntu3
libatk-adaptor (2.6.0-0ubuntu1) to 2.7.1-1
libatk-bridge2.0-0 (2.6.0-0ubuntu1) to 2.7.1-1
libatspi2.0-0 (2.6.0-0ubuntu1) to 2.7.1-1
libcogl-pango0 (1.10.4-0ubuntu1) to 1.12.0-1
libdee-1.0-4 (1.0.14-0ubuntu1) to 1.0.14-0ubuntu2
libgcrypt11 (1.5.0-3ubuntu1) to 1.5.0-3ubuntu2
libgcrypt11:i386 (1.5.0-3ubuntu1) to 1.5.0-3ubuntu2
libglibmm-2.4-1c2a (2.33.13-0ubuntu2) to 2.34.1-0ubuntu1
libgucharmap-2-90-7 (1:3.5.99-0ubuntu1) to 1:3.6.0-0ubuntu1
libgweather-3-1 (3.6.0-0ubuntu1) to 3.6.1-0ubuntu1
libgweather-common (3.6.0-0ubuntu1) to 3.6.1-0ubuntu1
libmessaging-menu0 (12.10.4-0ubuntu1) to 12.10.5-0ubuntu2
libnewt0.52 (0.52.11-2ubuntu12) to 0.52.11-2ubuntu13
libparted0debian1 (2.3-10ubuntu2) to 2.3-11ubuntu1
libpython3.3 (3.3.0-2) to 3.3.0-3
libpython3.3-minimal (3.3.0-2) to 3.3.0-3
libpython3.3-stdlib (3.3.0-2) to 3.3.0-3
libxml-libxml-perl (2.0006+dfsg-1) to 2.0010+dfsg-1
linux-generic ( to
meld (1.6.0-1) to 1.6.1-1
parted (2.3-10ubuntu2) to 2.3-11ubuntu1
pbuilder (0.208ubuntu1) to 0.213ubuntu1
python-dbus (1.1.1-1ubuntu1) to 1.1.1-1ubuntu2
python-dbus-dev (1.1.1-1ubuntu1) to 1.1.1-1ubuntu2
python-lxml (3.0.1-1) to 3.0.1-1build1
python-newt (0.52.11-2ubuntu12) to 0.52.11-2ubuntu13
python-pkg-resources (0.6.29-1ubuntu1) to 0.6.29-1ubuntu2
python-pyatspi2 (2.6.0+dfsg-0ubuntu1) to 2.7.1+dfsg-1
python3-dbus (1.1.1-1ubuntu1) to 1.1.1-1ubuntu2
python3-gdbm (3.3.0-1) to 3.3.0-1ubuntu1
python3-pkg-resources (0.6.29-1ubuntu1) to 0.6.29-1ubuntu2
python3.3 (3.3.0-2) to 3.3.0-3
python3.3-minimal (3.3.0-2) to 3.3.0-3
swig (2.0.7-3ubuntu1) to 2.0.8-1ubuntu1
swig2.0 (2.0.7-3ubuntu1) to 2.0.8-1ubuntu1
ubuntu-drivers-common (1:0.2.71ubuntu2) to 1:0.2.72
wget (1.13.4-3ubuntu1) to 1.14-1ubuntu1
whiptail (0.52.11-2ubuntu12) to 0.52.11-2ubuntu13
xml-core (0.13+nmu1) to 0.13+nmu2

Installed the following packages:
libcogl11 (1.12.0-1)
libegl1-mesa (9.0-0ubuntu1)
libgail-common (2.24.13-0ubuntu2)
libgbm1 (9.0-0ubuntu1)
libwayland0 (0.95.0-0ubuntu1)
libxcb-xfixes0 (1.8.1-2)
torchlight (1.0+2012+09+26-0ubuntu2)
I doubt it's due to Torchlight. EGL? Wayland? Any other ideas?