This is where Gentoo ZFS development is done. All useful changes made here are integrated with Gentoo's main tree after they have been properly validated. Only end users who have received explicit directions from ryao should use it. Those that have should switch back to the main tree as soon as they have been told that their issue has been fixed.
To add this overlay to a Gentoo system, run the following command:
layman -o https://raw.github.com/ryao/zfs-overlay/master/overlay.xml -f -a zfs
Note that you must have both dev-vcs/git and app-portage/layman installed on your system for this to work.
Please file bug reports for ebuilds in the portage tree in the Gentoo bug tracker and bug reports for ebuilds in this overlay on github.