Until april 2012 an existing Ubuntu was found by grub-mkconfig -o /boot/grub cfg "$@",
but after upgrading Ubuntu 11.10 (64-bit) to Ubuntu 12.04 the entryy for the upgraded
Ubuntu is missing in grub.cfg.
I must say that I do not use a special boot partition.
The only way to start Ubuntu 12.04 LTS Gnome is by Super Grub Disk (SGD 1!!).
I am using Sabayon Xfce.
Multi-boot includes XP/Pro, OpenSuSe 12.1, Ubuntu and the current Sabayon.