Recover from OS X Mountain Lion Installation Crash
A considerable number of people upgrading to OS X Mountain Lion (10.8) were surprised to learn that according to the OS X installer their hard drive was all of a sudden faulty and, according to Apple technicians, in need of replacement. The truth is the Mountain Lion installer has a bug that crashes the install process and then blames the hardware as faulty. Your hardware is likely fine, and here is how to recover your user data.