My car recently got a software upgrade as part of a service. Little did I think that it would bring a change I didn't want to the engine's characteristics--making it rougher and rortier--as well as fix the bugs it was supposed to. Here's the real wrench: I can't get it downgraded. Even though it must be possible, there's no procedure they'll enact for doing it. It's unthinkable that you can't get hardware back to where it started...so why the problem with software?
This incident reminded me of the nervousness I often have with upgrades and got me checking our policies and practicalities for Mathematica. Yes you can downgrade if you ever feel the need (though of course I certainly hope you don't).