Earlier this evening, I installed a command-line version of Debian Squeeze (i.e., still "testing" as of this writing) from the netinstall CD alongside a regular Ubuntu Karmic installation and had an issue with
GRUB that nearly had me cleaning my underwear.
Toward the end of the installation, the Debian installer told me that it saw I had Ubuntu installed and so would I want to install GRUB? It also assured me that it recognized that I had Ubuntu installed and that everything would be ok.
I've been through similar prompts with dual-boot installations before, and indeed everything has always gone just swimmingly. So, I said, "Sure." What I didn't know was that Squeeze is using the new and possibly-not-entirely-ready-for-prime-time GRUB 2. (I guess Karmic is as well.)
When I rebooted, GRUB gave me options for the new Squeeze install, but any trace of the Ubuntu install was gone. Hunting for /boot/grub/menu.lst gave me nothing. That's when I discovered that Squeeze installed GRUB 2 and most of the GRUB repair stuff on the Internet was obsolete. I was about the resort to drastic measures when
this post inspired me to try
# update-grub
and it worked.