Comment 18 for bug 969489

I'm getting the same symptom - more often than not getting dropped to the low-graphics alert during startup - and the change to /etc/init/lightdm.conf listed above has *not* made a difference. This behaviour is consistent across several different machines. From googling around this bug seems fairly prevalent, and is graphics vendor/chipset agnostic which supports your reasoning above. However as noted the prooposed change hasn't helped me.

Looking through logs in /var/log/lightdm the only thing that stands out is in the greeter logs e.g. for a failed start:
No protocol specified
No protocol specified
...
(unity-greeter:2340): Gtk-WARNING **: cannot open display: :0
No protocol specified
...

I'm happy to try out other ideas for fixes as this is a show stopper for a desktop environemnt refresh under way at work.