I can see that, especially if someone is administrating their own small site, and hasn't had experience in larger shops. But at the minimum (and since it is cheap enough) you should have at least 3 - 5 servers (esp. if you are making money off them) -- dev, test, staging, production, and failover. Just breaking the mirror to the failover box, and upgrading the primary would allow for an easy and quick backout procedure.

Oh, and there is another upgrade trick (I'll have to see if I still have my old writeup on it, and post it as a Gist). You can query the package manager, and make a few lists. First, list the packages (and versions) that are installed. Secondly, get a list of any file owned by a package that has changed since package installation (compare the file MD5 sum to the package's record of same). This should be a small list of files (mostly configuration related) that can be backed up. This gives you a good way to roll back changes if needed, and keep a system documented.

Finally, with Yum, you can roll back updates. Take a look at "yum history", and "yum history undo". This has saved me a couple times.