I read a great article on The Unofficial Apple Weblog [TUAW] about making a Mountain Lion installer on USB.
To make an installer version of Mountain Lion on USB you’ll obviously need a copy of the OSX Mountain Lion installer.
Next, go to your applications folder and find the actual installer…should be called Mac OS X Mount Lion.
Rich click that bad boy and select the Show Package Contents form the pop-up.
Navigate to Contents > SharedSupport and then start looking for the InstallESD.dmg.Â This is the image file for the installer.
Now we need to launch the DiskUtility so open a new folder with Command N.