I was wondering how your back-out plans look like. Untill now I must admit I never have had a really decent back-out plan in place when installing cumulative updates. I did ran into some issues sometimes, but usually those were fixable in a small amount of time inside of the outage window. But I would not have a good solution when the shit really hits the fan.
Theoretically speaking, would this suffice:
Restore pre-upgrade SQL back-ups of all databases
Restore pre-upgrade VM images of front-ends and back-ends
I cannot find a reason why it wouldn't, but since I haven't tried....
We're also running DocAve back-ups at the customer I'm at; but do those also revent SharePoint binaries? I assume they don't.