At URL I committed the latest virtualbox ebuilds containing a working implementation of the systemd service unit. Reproducible: Always
No response so far. Fixing in CVS and closing. + 27 Apr 2013; Fabio Erculiani <lxnay@gentoo.org> + virtualbox-guest-additions-4.2.12.ebuild, + +files/virtualbox-guest-additions.service: + add systemd unit, close bug #466148