The most recent experience I had here was with X-Swat proprietary drivers from the X-Swat PPA. Clearly, I made a mistake and installed a bad driver for my graphics card. Completely accepting the blame, I began a process I've done countless times in the past – purging all things Xorg and NVIDIA to get things back up and running.
You might be asking about the "bulletproof X" we've been told to use over the past year or so. In this situation, it wouldn't have fixed anything. After hours of repeating X/video driver cures that have always worked in the past, I remembered having a similar issue years ago...with my video card.
Looking back, I suspect the driver had hooks into something I was overlooking, but it wasn't worth the time to continue repeating "fixes" that clearly weren't working. If you have a working video driver, leave it the heck alone! And unless you're explicitly sure that video drivers from a PPA are going to fix something, avoid them!
Despite all the tips I've provided above, I believe there is something to be said for properly backing up your data. It's not merely just a good idea, if you value your current installation and the information contained within it, it's mandatory.
Now I should point out that these days, I rarely bother trying to back up my applications. To be honest, there's little reason to as I see it as a great opportunity to purge unneeded apps. Those I do need, will be re-installed easily when they're needed.
What's critical to save is the configuration data for those applications, most of which is in your home directory. Simply choosing to save the data within this directory can do more to get you back up and running than saving anything else. I compare it to having the media assets and database for a WordPress website – it's that important.
So what's the best way to protect these assets? Simple, find a means of backing things up that you'll actually do. Personally, I recommend local backups for the entire directory and perhaps more strategic backups for anything to be stored in the cloud. My logic behind this is both time and bandwidth. As for preferred services, there are countless ways to back up to either Amazon cloud servers, Google or even your own servers off site.
Cloud options range from SpiderOak, JungleDisk, UbuntuOne (ala Deja Dup), CrashPlan (for local backup too) and perhaps the best of them all, wuala. As for good local backup, it's really tough to beat rsync. If you're looking for something easy though, I'd point you to Déjà Dup.
No matter how you look at it, though, avoiding disaster and in turn, preventing a broken Ubuntu installation, begins and ends with you. Using the tips I've provided here, you'll be in a good starting place to avoid major problems and should something unexpected happen, hopefully you've heeded my warning about backing up today – not tomorrow.