This was taken from a few sources but it applies to the latest kernel update.
After I rebooted from the update pushed out on 8/19/11 I got the dreadedprompt.Code:grub>
System now boots properly. Open a terminal and type the following.Code:set root=(hd0,1) linux /vmlinuz root=/dev/sda ro initrd /initrd.img boot
Now you can reboot normally.Code:sudo grub-install /dev/sdZ sudo update-grub
I've lost count of how many times updates / upgrades do this but I'm really glad there was an easy solution.