I just committed a set of changes against the Gentoo Handbook (x86 and amd64) with the intent to have better instructions on GPT (GUID Partition Table) layout versus MBR (Master Boot Record) or MSDOS-style layout.
The part on "Preparing the Disks" saw the most changes. It starts with explaining the differences between the two layouts with advantages and disadvantages. It then helps the user decide what layout is best for him (or her).
Second, the example (and let me stress that one out again, because many people have reported bugs on it: it is an example) partition layout now includes a BIOS boot partition in the beginning, 2 MB in size. This is to support GRUB2 on GPT, but doesn't hurt for GRUB2 with the MSDOS-style layout either. That means that the partition numbers now move up one (the example /boot is now at sda2, the swap at sda3 and root on sda4).
The partitioning instructions now also include the proper alignment instructions (using MB alignment), and use parted as the default partitioning method.
The changes are submitted to CVS so will show up on the Gentoo site in an hour or so (documentation on the sites is synchronized hourly if I'm not mistaken). Please do give it a good read and report bugs on bugs.gentoo.org. You might also want to ping me on IRC if it is urgent, although no guarantees that I'm behind my computer at any point.