This is the most severe criticism I have for Ubuntu. It appears to be quite non-trivial to disable graphical boot. Ctrl+Alt+Backspace often breaks things. Ctrl+Alt+Fn does not switch to a text console. ./etc/init.d/gdm stop appears not to do anything. Annoying!
I just discovered that adding the word ‘text’ on the kernel command line (i.e., in your /boot/grub/menu.lst (oh wait, you’re probably using grub2; for now I’m downgrading, because I can’t stand having to remember two different inconsistent numbering schemes for my disk drives and partitions)) does something useful.