Comment 89 for bug 506717

I've found an workaround: adding "vga=792" at the end of the entry in /boot/grub/menu.lst (i'm using the old Grub, i've dist-upgraded since hardy, passing by all releases).
With that change, GDM appears correctly, the virtual terminals are ok and plymouth doesn't stays ugly (now it's displaying correctly, with Ubuntu logo. Before that, it was a purple screen with "ubuntu 10.04" written on it and a progress bar).
I'm seeing some people (with Nvidia cards) suffering with that problem too.