Stage 1 : working whilst tired, missed a critical dot in a command, removed system /etc/ instead of the local test ./etc/ of a root filesystem test build. Come home early to try to rescue the machine using /etc/ data from machines on the home network (same kernel, same users, same config).
Stage 2 : Get home, start up the office network, UPS alarm goes off, sparks and bang from my main machine, familiar smell of burnt electronics (again) and UPS seems now unable to provide any mains power, battery only.
Stage 3 : despite having the config, the broken laptop is still not fixed. Lots of packages are completely bust, resurrecting /etc/passwd, /etc/group and /etc/shadow from other machines at least provided login and chroot operation via the Lenny Debian installer. I don't want to have to reinstall this box but it is questionable whether setting everything up again after reinstalling is actually less work than fixing the broken config.
Result: My semi-VAC is ongoing, I'm back on my iBook laptop and I'm looking for a new UPS.