I've experienced the flickering screen problem which is caused by a rapidly restarting X server (on nvidia-chipset graphics). In earlier releases gdm seemed to

I've experienced the flickering screen problem which is caused by a rapidly restarting X server (on nvidia-chipset graphics). In earlier releases gdm seemed to throttle this after 5 attempts and present a text-mode dialog. By default now all is left to the xorg auto-discovery (no config file), so I assume that this fallback was no longer deemed necessary by the Ubuntu folks. I resorted to booting the computer with a usb-stick, temporarily disabling /etc/init/gdm.conf (or however that upstart-thing now is called, I forgot), then installing the morally questionable :-) nvidia-binary drivers via envy. Works great so far (under bare metal and via VirtualBox as a guest hosted by Windows7).