I just upgraded a F9 to F11 using the network install. After the successful install message, I rebooted to find the boot stuck on a grub prompt. After determining that somehow grub had not been installed properly, I used the rescue mode to re-install grub. When I then rebooted, I saw a blank (black) screen during the rhgb sequence, with just the multicolor progress bar moving from left to right. As the bar reached the right side, the standard F11 login screen appeared.
The system is an old Omnibook 8000 laptop. Here is my grub.conf
# grub.conf generated by anaconda
# Note that you do not have to rerun grub after making changes to this file
# NOTICE: You have a /boot partition. This means that
# all kernel and initrd paths are relative to /boot/, eg.
# root (hd0,0)
# kernel /vmlinuz-version ro root=/dev/VolGroup00/LogVol00
# initrd /initrd-version.img
title Fedora (126.96.36.199-64.fc11.i586)
kernel /vmlinuz-188.8.131.52-64.fc11.i586 ro root=UUID=9b55f5fd-a5d3-4408-8db7-0c64b0f6a7fa rhgb quiet