I recently started working on the sys-boot/grub package for Gentoo. The upstream project is preparing to release version 2.00, which is currently in beta.
If you are feeling adventurous, please give the new version of GRUB a try and report any bugs you find on bugs.gentoo.org. Keep a livecd handy; it is very possible to break your system.
There is a minimal guide on the Gentoo wiki, and a more in-depth page that could use some editor's love an care.
Additional documentation is available through Google or by running "info grub2" from your terminal.