root /etc #  emerge -uDN world

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

Calculating world dependencies... done!
[ebuild  N    ] app-arch/lzma-utils-4.32.5  462 kB 
[ebuild     U ] media-sound/alsa-headers-1.0.16 [1.0.14] 2,662 kB 
[ebuild     U ] net-misc/rsync-2.6.9-r6 [2.6.9-r5] USE="acl -ipv6 -static -xinetd" 0 kB 
[ebuild     U ] dev-util/desktop-file-utils-0.15 [0.14-r1] USE="-emacs" 341 kB 
[ebuild     U ] dev-libs/libxml2-2.6.31 [2.6.30-r1] USE="python readline -bootstrap -build -debug -doc -examples% -ipv6 -test" 4,624 kB 
[ebuild     U ] app-text/poppler-0.6.3 [0.6.1-r1] USE="jpeg zlib -cjk" 1,263 kB 
[ebuild     U ] sys-devel/m4-1.4.11 [1.4.10-r3] USE="nls -examples" 684 kB 
[ebuild  N    ] app-admin/sudo-1.6.8_p12-r1  USE="offensive pam -ldap (-selinux) -skey" 0 kB 
[ebuild  N    ] media-plugins/gst-plugins-libpng-0.10.6  0 kB 
[ebuild     U ] sys-devel/automake-1.10.1 [1.10] 897 kB 
[ebuild     U ] media-libs/alsa-lib-1.0.16 [1.0.14a-r1] USE="midi -alisp -debug -doc" ALSA_PCM_PLUGINS="adpcm alaw asym%* copy dmix%* dshare dsnoop empty%* extplug file hooks iec958%* ioplug%* ladspa lfloat linear meter mulaw multi null plug%* rate route share shm softvol%*" 764 kB 
[ebuild     U ] sys-apps/coreutils-6.10-r1 [6.9-r1] USE="acl nls (-selinux) -static -xattr" 3,670 kB 
[ebuild   R   ] net-irc/weechat-0.2.6  USE="perl python ruby* spell ssl -debug -lua" 0 kB 
[ebuild   R   ] dev-lang/swig-1.3.31  USE="java perl php python ruby* -doc -guile -lua -mono -ocaml -pike -tcl -tk" 0 kB 
[ebuild     U ] media-sound/alsa-utils-1.0.16 [1.0.14] USE="midi nls" 992 kB 
[ebuild   R   ] gnome-base/gnome-vfs-2.20.1-r1  USE="acl avahi* hal ssl -debug -doc -gnutls -ipv6 -kerberos -samba" 0 kB 
[ebuild     U ] media-sound/exaile-0.2.13 [0.2.11.1] USE="aac alsa gnome ipod jpeg libsexy mad nls ogg oss png%* vorbis -cdparanoia -equalizer* -flac -libnotify -musepack" 1,239 kB 
[ebuild  N    ] xfce-base/thunar-0.9.0-r2  USE="X dbus gnome hal pcre startup-notification trash-plugin -debug -doc -exif" 0 kB 
[ebuild  N    ] kde-misc/kdnssd-avahi-0.1.2  USE="xinerama -arts -debug" 0 kB 
[blocks B     ] sys-apps/mktemp (is blocking sys-apps/coreutils-6.10-r1)
[blocks B     ] >=sys-apps/coreutils-6.10 (is blocking sys-apps/mktemp-1.5)

Total: 19 packages (11 upgrades, 5 new, 3 reinstalls, 2 blocks), Size of downloads: 17,594 kB

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

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