As you probably have noticed, we are now forcing people to *run* systemd to be able to properly run Gnome 3.8, otherwise power management and multiseat support are lost, also gdm needs the way of taking care of cgroups implemented in systemd to be restarted properly.
After spending a lot of time trying to let logind run without systemd (thanks a lot to lxnay specially for his effort with systemd-love overlay, also to WilliamH and qnikst to try to improve openRC, ssuominen for trying to make udev ebuild take care of logind, and to mgorny for making systemd work nice on Gentoo... and probably others I am forgetting now :S), all the efforts failed because systemd-205 no longer let us run logind alone as cgroups handling was moved to systemd itself. Previously, a lot of the work was done by Ubuntu/Debian people, but now looks like they don't have a "fix" for this new (and hard to handle) situation in the short term (apart of sticking with systemd-204 for a long time like they did in the past with udev-175).
Regarding systemd status on Gentoo, in some cases, unit files are present in testing packages, but there are more packages still missing unit files blocking https://bugs.gentoo.org/show_bug.cgi?id=448882
If you want to help, you can try to find unit files in other distributions like opensuse, fedora, Arch, Mageia and try to make them work on Gentoo. In that case would be nice if you could report the bug and make it block bug 448882.
Apart of that, you can follow http://wiki.gentoo.org/wiki/Systemd