When I upgraded to Kubuntu 12.04 I encountered a showstopper bug in the proprietary binary nVidia drivers included in the repositories. As confirmed on the nVidia site, there was a regression (a bug that removes functionality that was previously present) whereby 3D graphics and compositing became incredibly slow. And when I say slow, I mean that it would take in the region of 10 minutes to display the preview of an application in the task bar.
After searching online and coming across quite a few people who were affected by the same bug, I decided to try out the open source Nouveau drivers. I was pleasantly surprised, as the drivers seem to support most, if not all of the compositing effects. Unfortunately they are still far from perfect. They are slow, taking up to 10 seconds to show some effects that should take 1 or 2 seconds. In addition to being slow, they seem to crash from time to time, when the compositing gets too much for them.
While the sluggish effects and the crashes only happen about 10% of the time, the crashes themselves forced a hard reboot, not only making me extremely frustrated, but also putting a serious dent in my productivity. I even waited and waited for Canonical to upload a fixed version o the driver, but after 2 weeks, that didn't seem to be happening. Eventually it just got too much for me, and last night I decided to see if the latest version of the nVidia drivers on their site exhibited the same problem.
Some of the forum posts and blogs I came across mentioned that the latest version didn't fix their problem, but others reported success, so while I was hesitant to install them I figured that I'd be no worse off than I already was. I went ahead and downloaded the drivers, after having to fiddle around with their platform/architecture/model selector.
The first thing you need to do when you want to install the drivers is to stop X.org (the GUI) and run the driver installer file without from the command line. To do this, you need to log out not shut down!) and on the login screen select the "console login" option from one of the menus. Once you have a console login prompt in front of you, login using your normal user details, and then run sudo /etc/init.d/kdm stop to stop X.org.
If, like me, you have the Nouveau driver installed, the nVidia driver installer will uninstall it and blacklist it. You will have to reboot after that. Once you have rebooted, you will need to go to a console login and stop X.org again.
To run the installer, simply go to where you downloaded it to, and run sudo sh NVIDIA-Linux-x86_64-295.49.run and follow the prompts that appear. Once the installer has run, reboot and you should boot into your new, slick, and bugfree drivers!