I never trust it either, so I tar up the entire site, export the db,
then upgrade.

Worst cases leaves me with re-importing the working db, and untaring the old files to restore.
The worst part is if we have a problem and several weeks go by before it's noticed...that is what I worry about. The worst one was when we used the pre-release of phpbb2. Our db was running in a funky state for a couple months.