I went through and removed all the gnome stuff that I could get away with:

Start-Date: 2012-05-28  03:27:46
Commandline: synaptic
Install: compiz-kde:amd64 (0.9.7.8-0ubuntu1, automatic), compizconfig-backend-kconfig:amd64 (0.9.2-0ubuntu1, automatic)
Remove: python-keyring:amd64 (0.7.1-1fakesync1), unity:amd64 (5.12-0ubuntu1), metacity:amd64 (2.34.1-1ubuntu11), ubuntu-docs:amd64 (12.04.5), gir1.2-ubuntuoneui-3.0:amd64 (3.0.0-0ubuntu1), tumbler:amd64 (0.1.24-0ubuntu1), system-config-printer-gnome:amd64 (1.3.8+20120201-0ubuntu8), libtumbler-1-0:amd64 (0.1.24-0ubuntu1), ubuntuone-client:amd64 (3.0.0-0ubuntu1), zenity:amd64 (3.4.0-0ubuntu4), libgnome-control-center1:amd64 (3.4.1-0ubuntu2), libgtk2-perl:amd64 (1.223-1build3), gnome-settings-daemon:amd64 (3.4.1-0ubuntu1.1), unity-scope-musicstores:amd64 (5.12.0-0ubuntu1), gnome-session-common:amd64 (3.2.1-0ubuntu8), python-launchpadlib:amd64 (1.9.12-1), indicator-applet:amd64 (0.5.0-0ubuntu1), python-gnomekeyring:amd64 (2.32.0+dfsg-1), usb-creator-gtk:amd64 (0.2.38), indicator-applet-complete:amd64 (0.5.0-0ubuntu1), gnome-control-center-data:amd64 (3.4.1-0ubuntu2), gnome-keyring:amd64 (3.2.2-2ubuntu4), libpango-perl:amd64 (1.222-1build1), rhythmbox-ubuntuone:amd64 (3.0.0-0ubuntu1), sessioninstaller:amd64 (0.20+bzr128-0ubuntu1), ubuntu-sso-client-gtk:amd64 (3.0.0-0ubuntu2), tumbler-common:amd64 (0.1.24-0ubuntu1), indicator-power:amd64 (2.0-0ubuntu1), libsyncdaemon-1.0-1:amd64 (3.0.0-0ubuntu1), compiz-gnome:amd64 (0.9.7.8-0ubuntu1), desktop-base:amd64 (6.0.7ubuntu1), python-gi-cairo:amd64 (3.2.2-1~precise), libglib-perl:amd64 (1.241-1), python-ubuntu-sso-client:amd64 (3.0.0-0ubuntu2), network-manager-pptp-gnome:amd64 (0.9.4.0-0ubuntu1), ubuntu-sso-client:amd64 (3.0.0-0ubuntu2), libubuntuoneui-3.0-1:amd64 (3.0.0-0ubuntu1), yelp:amd64 (3.4.1-0ubuntu1), indicator-session:amd64 (0.3.96-0ubuntu1), zenity-common:amd64 (3.4.0-0ubuntu4), indicator-datetime:amd64 (0.3.94-0ubuntu2), gnome-control-center:amd64 (3.4.1-0ubuntu2), python-apport:amd64 (2.0.1-0ubuntu7), gnome-user-guide:amd64 (3.4.1-1), gnome-online-accounts:amd64 (3.4.0-0ubuntu1), compiz:amd64 (0.9.7.8-0ubuntu1), libpam-gnome-keyring:amd64 (3.2.2-2ubuntu4), python-gconf:amd64 (2.28.1+dfsg-1)
End-Date: 2012-05-28  03:31:55

Start-Date: 2012-05-28  03:41:54
Commandline: synaptic
Remove: libyelp0:amd64 (3.4.1-0ubuntu1), libnm-gtk0:amd64 (0.9.4.1-0ubuntu2), libgoa-1.0-0:amd64 (3.4.0-0ubuntu1), evolution-data-server:amd64 (3.2.3-0ubuntu7), libgoa-1.0-common:amd64 (3.4.0-0ubuntu1)
End-Date: 2012-05-28  03:41:59

Start-Date: 2012-05-28  03:49:02
Commandline: synaptic
Install: polkit-kde-1:amd64 (0.99.0-3ubuntu5, automatic)
Remove: policykit-1-gnome:amd64 (0.105-1ubuntu3), jockey-gtk:amd64 (0.9.7-0ubuntu7)
End-Date: 2012-05-28  03:49:13

With xdm installed, my /var/log/ConsoleKit/history entry looks like:

1338187484.617 type=SEAT_SESSION_REMOVED : seat-id='Seat1' session-id='Session1' session-type='' session-x11-display='' session-x11-display-device='' session-display-device='/dev/tty1' session-remote-host-name='' session-is-local=TRUE session-unix-user=1000 session-creation-time='2012-05-28T06:34:47.893356Z'
1338187484.628 type=SEAT_ACTIVE_SESSION_CHANGED : seat-id='Seat1' session-id=''
1338187539.607 type=SEAT_ADDED : seat-id='Seat1' seat-kind=0
1338187539.969 type=SEAT_ADDED : seat-id='Seat2' seat-kind=1
1338187540.015 type=SEAT_SESSION_ADDED : seat-id='Seat2' session-id='Session1' session-type='' session-x11-display=':0' session-x11-display-device='' session-display-device='' session-remote-host-name='' session-is-local=TRUE session-unix-user=1000 session-creation-time='2012-05-28T06:45:39.966867Z'

Without xdm, launching startx from tty1

1338186743.270 type=SEAT_SESSION_REMOVED : seat-id='Seat1' session-id='Session3' session-type='' session-x11-display=':0' session-x11-display-device='/dev/tty7' session-display-device='/dev/tty1' session-remote-host-name='' session-is-local=TRUE session-unix-user=1000 session-creation-time='2012-05-28T06:15:13.370623Z'
1338186743.285 type=SEAT_ACTIVE_SESSION_CHANGED : seat-id='Seat1' session-id=''
1338186743.310 type=SEAT_SESSION_REMOVED : seat-id='Seat1' session-id='Session1' session-type='' session-x11-display='' session-x11-display-device='' session-display-device='/dev/tty1' session-remote-host-name='' session-is-local=TRUE session-unix-user=1000 session-creation-time='2012-05-28T06:07:49.977281Z'
1338186887.804 type=SEAT_ADDED : seat-id='Seat1' seat-kind=0
1338186887.905 type=SEAT_SESSION_ADDED : seat-id='Seat1' session-id='Session1' session-type='' session-x11-display='' session-x11-display-device='' session-display-device='/dev/tty1' session-remote-host-name='' session-is-local=TRUE session-unix-user=1000 session-creation-time='2012-05-28T06:34:47.893356Z'
1338186887.913 type=SEAT_ACTIVE_SESSION_CHANGED : seat-id='Seat1' session-id='Session1'