OS X Tutorials: Upgrade to Mountain Lion This interactive book will guide you on the journey to Mountain Lion, with the help of video tutorials.
Most users do not experience issues when upgrading to a new operating system, but a small minority does. If you’re unlucky enough to be in that small minority, then it could seriously disrupt your daily activities. You should also consider whether upgrading to Mountain Lion as an early adaptor is right for you. This is especially important if you use your computer to make money or for other critical activities, such as writing a thesis. It’s normally a good practice to wait at least a month after a major update of an operating system and let others find the major issues first.
You'll learn how to upgrade to Mountain Lion, do a clean install, create a rollback strategy to be able to revert to OS X Lion and how take Mountain Lion for a spin around the block, without impacting your current work and setup, by running it in its own sandbox.