Are people actually doing this for any serious production systems?

> ... there is always a chance that you may experience problems rebooting your system after the upgrade

This doesn't give me confidence in the process. Don't get me wrong, Debian (and derivatives) are great systems, but the lack of any real rollback option and notes like this right at the beginning of upgrade docs just scream "don't do that, just do a fresh install". Which is probably a good advice.