First hint: it's a mess -- don't do it on a critical machine. (My main machine is ~amd64 and that's why I'm doing it on virtual ~amd64 machines first.)
The new gnome-shell demands that systemd be installed, even if you don't intend to use it. The latest systemd conflicts with udev because the udev project has been rolled into systemd, which now provides all of the files previously installed by udev. Therefore your machine will still boot without udev because systemd installs all the udev files. You don't need to start or use systemd if you don't want to, but the systemd package must be installed *before* you reboot and after removing udev. Removal of udev has caused a few (temporary) problems with useflags, because a few packages still depend directly on udev instead of the newer (!systemd ? udev) which means accept either one but not both. That will get fixed soon, I'm sure. The right way to upgrade gnome is probably to remove every gnome package on the machine, which will avoid many of the conflicts I've had to fight for the last two days -- but of course I did it the hard way instead :) You can try emerge -au gnome-light early in the update, which is simpler than emerging gnome in all its immensity, but that's no guarantee of success -- I'm sure you'll still run into conflicts between packages and useflags, but it might be a bit easier. When you see conflicting packages that won't install, I suggest deleting both packages immediately -- let portage sort out the conflicts. Just keep removing packages until portage finally stops complaining. Beware of pambase, however. I finally took Canek's advice and removed consolekit from the machine and unset the useflag for all packages, including pambase and polkit. I'd suggest you get pambase and polkit re-installed with the proper useflags before you try to reboot. Dunno if that's mandatory, but I did it that way and had no problems (yet). I've finished updating my virtual gentoo systemd machine now, but I'm still fighting with the virtual openrc machine and I'm not sure how it will turn out. More tomorrow :)
