eselect news list, says that sys-fs/udev-181 will be unmasked on 2012-03-19. It's still masked. As is sys-apps/openrc-0.9.9 which is required for sys-fs/udev-181. Reproducible: Always
Make sure your portage tree is up to date. Neither udev nor openrc are masked.
Maybe I used the wrong term. "mask" may not be the right term. sys-fs/udev-128-r3 (and sys-apps/openrc-0.9.9.3) are both in "~amd64". This means they are both in the "testing" branch, not stable. I thought this news item meant that these packages were being marked as stable. Guess I just misunderstood the terms, sorry.