I notice that for the PPC install, there is a need to exit the chroot before installing yaboot to mount -o bind /sys /mnt/gentoo/sys. Why not move this to the step where everything else is mounted so that there are fewer steps and therefore fewer chances for mistakes. I think this would make things a little smoother.
We don't really want to do that because the mount points are created when unpacking the install files in the step after mounting. Although it seems like it would be better to do all of the mounts at the same time, by moving it to later in the documentation (when needed), we allow the correct static /dev entries and .keep files to be created by unpacking the install files. Mounting earlier would cause those files to be written to the mounted fs, which isn't what we want. It's a nice idea, but not quite right. :) Feel free to reopen if you disagree, or make a new bug if you find any other potential issues, it's nice to get other people's opinions on the docs.