Yesterday I upgraded from Ubuntu Edgy Eft to Ubuntu Feisty Fawn (which is not yet released, usual disclaimers apply, don't use it or it will poison your hamster etc.)
Upgrades are harsh environments for a computer; they're the computing equivalent of replacing the engine in your car. Even in skilled hands, things can go wrong, and you don't want to get an error message telling you anything went wrong, even if it seems innocuous, because your computer might be about to give up the ghost completely. (This is the computing equivalent of watching a mechanic walk over to you slowly from your car. This man is a heavyset man in grease-blackened denims, wiping his hands with a red rag, looking down at the ground, walking slowly while he tries to get a read on how you're going to react to the news of your car's impending trip to the scrapyard.)
Thus, before I began this process, so fraught as it is with the risk of doom, it was with great pleasure that I pushed the "snapshot" button on my VMware application. If doom happens, I can just undo it. (In this case, doom did not happen. Feisty Fawn is running right now. Ubuntu is really a joy.)
You may not have used virtualization software yet. You might be thinking about how slow it makes things, how you don't want to have even more complexity in your computing environment. Forget all that.
VMware is awesome. I have allocated 512MB to my VMware instance, which is running on my solo-core uniprocessor laptop. I can run all of my usual productivity applications, compile and build packages for software, run my D&D software (most of which is written in Java). I can even watch high-resolution video, with audio, and get a decent rate, and that's inside the guest. If I wanted to play a fullscreen immersive game, I might use the host computer for that, but that's OK; that's what it's there for. (I use a Windows host, mostly because it's the default OS of this laptop.)