# emerge --update --newuse --deep --with-bdeps=y -av world

These are the packages that would be merged, in order:

Calculating dependencies... done!
[ebuild     U  ] x11-libs/pixman-0.28.2 [0.28.0] USE="mmx sse2 (-altivec) (-iwmmxt) (-neon) -static-libs" 611 kB
[ebuild  NS    ] sys-kernel/gentoo-sources-3.6.10:3.6.10 [3.6.8:3.6.8] USE="-build -deblob -symlink" 239 kB
[ebuild  N    #] sys-fs/eudev-1_beta1  USE="gudev hwdb keymap modutils openrc -doc -introspection -kmod (-selinux) -static-libs" 1,589 kB
[blocks B      ] sys-fs/udev ("sys-fs/udev" is blocking sys-fs/eudev-1_beta1)

Total: 3 packages (1 upgrade, 1 new, 1 in new slot), Size of downloads: 2,438 kB
Conflict: 1 block (1 unsatisfied)

 * Error: The above package list contains packages which cannot be
 * installed at the same time on the same system.

  (sys-fs/udev-196-r1::gentoo, installed) pulled in by
    sys-fs/udev[gudev] required by (gnome-base/gnome-settings-daemon-3.4.2::gentoo, installed)
    >=sys-fs/udev-196-r1[acl,gudev,hwdb,keymap] required by (virtual/udev-196::gentoo, installed)
    >=sys-fs/udev-142 required by (media-video/vlc-2.0.4::gentoo, installed)
    sys-fs/udev[gudev] required by (media-gfx/gimp-2.8.2-r1::gentoo, installed)

  (sys-fs/eudev-1_beta1::gentoo, ebuild scheduled for merge) pulled in by
    >=sys-fs/eudev-1_beta1[gudev,hwdb,keymap] required by (virtual/udev-196::gentoo, installed)


For more information about Blocked Packages, please refer to the following
section of the Gentoo Linux x86 Handbook (architecture is irrelevant):

http://www.gentoo.org/doc/en/handbook/handbook-x86.xml?full=1#blocked


The following mask changes are necessary to proceed:
#required by virtual/udev-196, required by www-client/google-chrome-23.0.1271.95_p169798, required by @selected, required by @world (argument)
# /etc/portage/package.mask:
# beta udev alternative
=sys-fs/eudev-1_beta1

The following USE changes are necessary to proceed:
#required by virtual/udev-196, required by www-client/google-chrome-23.0.1271.95_p169798, required by @selected, required by @world (argument)
=sys-fs/eudev-1_beta1 gudev keymap hwdb

NOTE: The --autounmask-keep-masks option will prevent emerge
      from creating package.unmask or ** keyword changes.

Use --autounmask-write to write changes to config files (honoring CONFIG_PROTECT).