Making "default saved" work with GRUB2...?

The correct syntax for enabling savedefault in /etc/default/grub (GRUB 2) is with the lines:

GRUB_DEFAULT=saved
GRUB_SAVEDEFAULT=true

and not with the line DEFAULT=save that the enquirer suggested.

After adding the two lines above to /etc/default/grub, one has to update GRUB's configuration, as a superuser, with the following commands:

grub-mkconfig
update-grub

At least on Lubuntu 12.10, grub-mkconfig is not needed (as it, without options, dumps the config file to stdout). The only needed command is update-grub which actually invokes grub-mkconfig with the proper -o file option.