The recent instability problems seem to have been caused by the root disk in the server – as it has now failed completely.
I have purchased new hardware and am switching distribution (from Gentoo to Ubuntu) in order to avoid having to compile everything, and also because Gentoo has failed to deliver any kind of stability in recent times.
At this point I have several services up and running, most notably the Apache/MySQL combo enabling me to write this. Next up will be all the mail related services and dependencies thereof (such as the LDAP server), followed by the remaining web services (Tomcat, Subversion and Webmail).
I expect the remaining services to be more or less restored within the next 24 hours, but keep an eye out for updated status reports here.