It may sound obvious, but prior to any upgrade – prepare for the eventuality of a system rebuild. I hit an upgrade today that required both a Recovery CD partition swap and file system check on the original Active Partition to recover the system, after SELinux failures occurred after a switch-version.
For a rebuild, collect the following from CLI prior to upgrade:
show network eth0
show version active
utils ntp config
This will collect IP/Hostname, DNS, NTP/Timezone, firmware and certificate details(last one is critical!).
This is all negated if you have Answer Files set up to begin with and/or are using PCD.