I have Xubuntu 12.10 running fine on a Thinkpad T60. Grub2 is installed as the boot manager and the GRUB....LINUX_DEFAULT is set as "quiet splash". Therefore, Grub should display its splash image until plymouth takes over, as I understand it. Unfortunately, it does not. If I hold down shift to get into the boot menu, my splash image shows up, but the screen remains black. I realise it's a minor cosmetic issue, but I have found no way to fix it.
First of all, the GRUB splash displays behind the text of the kernel and OS selection screen that you get to by holding Shift during boot. It does not show up by default (unless you are dual booting, although I do not own a copy of windows to my name and am not sure of this) and I don't think it works as a traditional splash (like Plymouth; please someone more knowledgeable correct me here if I am wrong).
To make the GRUB menu (and your picture in the background) show up you need to edit the file