Ubuntu Quantal, scheduled to be released this October, will ship with GRUB as the default bootloader. Previously Canonical had plans to drop GRUB and use other bootloaders instead. The main cause was Ubuntu chief Mark Shuttleworth couldn't trust the Free Software Foundation. Also, for the secure boot feature to work, some amount of non-free code had to be included in the bootloader, which is prohibited by GPL.
Colin Watson announced in Ubuntu devel mailing list:
Following extensive discussions within Canonical, with our OEM partners, and with various other groups including the FSF, we've decided to use the GPLv3-licensed GRUB 2 boot loader by default on systems with UEFI Secure Boot, to match our behavior on all other x86 systems.
To mitigate the issues with preinstalled systems that we talked about previously, we'll be adding compulsory test cases to ensure that Canonical validates that every system we test has an option to disable secure boot and an option to install user certificates; and we will retain fallback plans involving efilinux in the case of serious error, although we hope we won't need to use them.
Ubuntu 12.10 will ship with GRUB 2.00 and to ensure that secure boot works, some patches from Fedora bootloader will be applied. Thus, it will be mainly a signed version of GRUB capable of running in an UEFI environment.