The elog message regarding the xorg.conf.conf (this is a typo, it should be xorg.conf.vbox) is outdated. The file comes with an input section for "vboxmouse" which is not used anymore as the drivers have been removed and everything is handled by the evdev driver. I think the only part that makes sense is to keep the screen section that uses the "vboxvideo" driver.
+ 17 Nov 2012; Lars Wendler <polynomial-c@gentoo.org> + virtualbox-guest-additions-4.1.22.ebuild, + virtualbox-guest-additions-4.2.2.ebuild, + virtualbox-guest-additions-4.2.4.ebuild, files/xorg.conf.vbox: + Fixed elog message to no longer mention the deprecated (and removed) + virtualbox mouse driver. Adjusted the sample xorg.conf file accordingly (bug + #443608). +