http://www.gentoo.org/doc/en/handbook/handbook-x86.xml?full=1#blocked should explain what things like [blocks B ] <media-video/mplayer-bin-1.0_rc1-r2 (is blocking app-emulation/emul-linux-x86-medialibs-10.2) mean - I'm tired of explaining it :p
Uhh....it does. Here's what the text below the example in that section says about why one package blocks another, and how to deal with it. "Ebuilds contain specific fields that inform Portage about its dependencies. There are two possible dependencies: build dependencies, declared in DEPEND and run-time dependencies, declared in RDEPEND. When one of these dependencies explicitly marks a package or virtual as being not compatible, it triggers a blockage. To fix a blockage, you can choose to not install the package or unmerge the conflicting package first. In the given example, you can opt not to install postfix or to remove ssmtp first. It is also possible that two packages that are yet to be installed are blocking each other. In this rare case, you should find out why you need to install both. In most cases you can do with one of the packages alone. If not, please file a bug on Gentoo's bugtracking system." Not a bug, closing.
Note the '<' in '<media-video/mplayer-bin-1.0_rc1-r2' Updating the blocking package to a more recent version would remove the block. That option is not mentioned.
You're right, I missed the atom in the blocker. Will add something on this.
Thanks for reporting & for the clarification. Fixed in CVS.
