Unable to log in because of "missing" unity-greeter

I'm not quite sure if the title is right because unity-greeter is there but the interface doesn't appear sometimes.

Basically, I press the power button on my Samsung Series 9 notebook, get a short purple flash and then a black screen with a cursor blinking in the top left part of the screen and a moveable mouse cursor.

The FN keys all seem to work and the drums welcome sound is audible as well.

Roughly I'd say that I need 5 to 6 attempts to boot. I've seen some very weird log messages in /var/log/lightdm/lightdm.log

Added logs to bug report.

It seems like it would try to automatically authenticate but fails. It shouldn't try to auto-login though.

Steps to reproduce:
Unknown yet

ProblemType: Bug
DistroRelease: Ubuntu 13.04
Package: unity-greeter 13.04.1-0ubuntu2
ProcVersionSignature: Ubuntu 3.8.0-9.18-generic 3.8.1
Uname: Linux 3.8.0-9-generic x86_64
ApportVersion: 2.9-0ubuntu2
Architecture: amd64
Date: Sun Mar 3 13:28:39 2013
InstallationDate: Installed on 2013-02-13 (18 days ago)
InstallationMedia: Ubuntu 13.04 "Raring Ringtail" - Alpha amd64 (20130212)
MarkForUpload: True
ProcEnviron:
 TERM=screen
 PATH=(custom, no user)
 XDG_RUNTIME_DIR=<set>
 LANG=en_US.UTF-8
 SHELL=/bin/bash
SourcePackage: unity-greeter
UpgradeStatus: No upgrade log present (probably fresh install)