KDE is split in too many ebuilds, which is one of reasons for slow emerge. there could be one ebuild for each source package listed at http://kde.org/info/4.8.4.php
You can check the old split-ebuilds guide[1] to learn why KDE moved to the split ebuilds. In case you aren't aware, KDE upstream has been moving to split tarballs and that trend continues with KDE-4.9 (where most modules will be split) and with KF5, even kdelibs might be split. [1] - http://sources.gentoo.org/cgi-bin/viewvc.cgi/gentoo/xml/htdocs/proj/en/desktop/kde/kde-split-ebuilds.xml?hideattic=0&view=markup So WONTFIX.