I just ran "emerge mysql" to upgrade my system from MySQL4 to MySQL5, and then discovered that every program that was linked to MySQL broke (complaining about being unable to find the v4 libraries.) As someone relatively new to Gentoo perhaps this is expected behaviour, but I expected that Portage would realise there were programs that depended on MySQL, and either upgraded or recompiled them as part of the MySQL upgrade process. Is this a bug in the MySQL ebuild, or functionality that is not yet implemented in Portage?
http://www.gentoo.org/doc/en/mysql-upgrading.xml