I suggest there is a bug in app-admin/eselect-boost with a multi boost installation. Here with boost-1.41.0-r3 and boost-1.35.0-r5. I told eselect to use boost-1.41.0-r3, because boost::this_thread::yield() was introduced with >=boost-1.39. After purging boost-1.35.0-r5 everything went fine. Please see http://bugs.gentoo.org/show_bug.cgi?id=332683 for further details. Reproducible: Always
This is not a bug in eselect or boost, the package in questions mixes different version of boost headers and libs. See bug 332683 comment 13.