...and it's probably worth mentioning the nice pre-checking script that a certain forum user efahl shared a couple of weeks ago that may be very useful on actual x86 hardware.
It will provide some reassurance if you need to be more careful about upgrade downtime on real-life hardware than on a VM (where you can simply roll back to a VM snapshot if something goes wrong and not get shouted at for too long)
pkg-scan.sh upgrade pre-check script post by .efahl.
a VERY very useful script I've used about 30 times in the last 2 weeks - many thanks