Very nice! I'd been using the ebuilds from gentoo-china, but the Cairo from there was very ugly: lots of color fringing. These ebuilds and patches from bi3l are perfect. I am now using all stock Portage ~amd64 except for the four ebuilds from bi3l here.
What's the hold-up getting this stuff put in the official Portage tree? Seems totally stable. And if they claim it's a legal issue, well so is the BCI hinter in freetype, but they don't seem to have a problem with that!
Now if only someone would implement fractional metrics in freetype. It's great that we can render glyphs with subpixel precision, but we should not be constrained to positioning them at whole-pixel boundaries!
Also, why the apparent lack of kerning in libXft? If you look at "AVAVA" in Corbel 12 pt. in a libXft-rendered program, it's much more spaced out than if you look at it in a Cairo-rendered program. I've also noticed that libXft doesn't do ligatures: compare "fi" in a libXft program versus in a Cairo program.