Comment 2 for bug 416772

We probably oughtn't to expose this to any significant number of users until said kernel issue is resolved. For details, see:

  https://lists.ubuntu.com/archives/kernel-team/2009-August/006773.html

Note that there are more configuration files available than just /etc/default/grub, although they're harder work to edit (that's why /etc/default/grub exists, with the easy options), so you do have a workaround available: you can edit /etc/grub.d/10_linux, look for the linux_entry function definition, and add whatever gfxpayload line you like just before the "linux ${rel_dirname}/..." line.