After fresh install of oneiric 11.10 nothing displayed during boot process, but I still can switch to tty's. I made apt-get update/upgrade from tty and tried to reboot. Nothing changed. 'service lightdm restart' and 'startx' also doesn't help.
UPD(24.10.2011): Just reported bug with apport-bug to launchpad. You can see there logs and others collected reports.
Best Answer
Try
sudo apt-get purge nvidia
replace nvidia by the driver you are using. It will use the free driver Nouveau.That worked for me.