Moving to GRUB2 my Arch Linux no longer resumes from hibernation, because the actual resuming is no longer set up. In GRUB legacy I'd write:
kernel /vmlinuz26 root=/dev/disk/by-uuid/X ro resume=/dev/disk/by-uuid/Y ro
But with GRUB2's new way of handling the boot menu, I no longer know how, where and in which form to add this. My guess is you'd add the entire menuentry to /etc/grub.d/40_custom/ and somehow set up the resuming there? Manually hardcoding menuentries into GRUB2 seems to go against its flexible menu generation approach, but whatever reenables me to use hibernate is gladly welcomed.