betelgeuse@pena /usr/portage/sci-libs/hdf5 $ grep built_with_use * hdf5-1.6.5-r1.ebuild: && built_with_use sys-devel/gcc fortran ; then hdf5-1.6.6.ebuild: if use mpi && ! built_with_use sys-cluster/mpich2 pvfs2 ; then hdf5-1.6.6.ebuild: if built_with_use sys-cluster/mpich2 pvfs2 ; then hdf5-1.6.7.ebuild: if use mpi && ! built_with_use sys-cluster/mpich2 pvfs2 ; then hdf5-1.6.7.ebuild: if built_with_use sys-cluster/mpich2 pvfs2 ; then All these have keywords in 1.8.4-r1 so on that regard it's safe to remove them.
Packages using built_with_use were removed from tree. Thanks!