Читал тут новости пришедшие с синком.
tl;dr
Если у вас /usr отдельным разделом и нету initrd, то после апдейтов udev'а от 19 марта система станет небутабельной.
Лично я пользуюсь genkernel'ом и мой /usr не отделён от корня, зависимость есть, брат жив.
2012-03-16-udev-181-unmasking
Title udev-181 unmasking
Author William Hubbs <williamh@gentoo.org>
Posted 2012-03-16
Revision 1
udev-181 is being unmasked on 2012-03-19.
This news item is to inform you that once you upgrade to a version of
udev >=181, if you have /usr on a separate partition, you must boot your
system with an initramfs which pre-mounts /usr.
An initramfs which does this is created by
>=sys-kernel/genkernel-3.4.25.1 or
>=sys-kernel/dracut-017-r1. If you do not want to use these tools, be
sure any initramfs you create pre-mounts /usr.
Also, if you are using OpenRC, you must upgrade to >= openrc-0.9.9.
For more information on why this has been done, see the following URL:
http://freedesktop.org/wiki/Software/systemd/separate-usr-is-broken
