Sooner or later almost any Linux admin feel the need for a history of configuration changes. May it the X server configuration which got corrupted while you experimented with the Composite extension and OpenGL or may it the apache configuration you jumbled while updating the popular web server.

Gentoo Linux brings some powerful tool's (dispatch-conf, etc-update) out of the box to manage and update those configuration files. dispatch-conf is even able to store older versions inside of /etc/config-archive with RCS, but dealing with this ancient VCS is't that much fun and self written config files are not included by default.

SVK is the answer.