ScottishDuck posted a guide on MacRumors: How to create a bootable USB Stick with Apple Mac OSX 10.8 Mountain Lion GM (Golden Master). The process is quite easy:
* Show Package Contents -> mount InstallESD.dmg
* “restore” BaseSystem.dmg to your USB drive
* System -> Installation -> Delete the link called “Packages” and then create a new folder with the same name
* Copy all the Packages to the USB Disk
* cp /Volumes/Mac\ OS\ X\ Install\ ESD/mach_kernel /Volumes/lionUSBinstaller/.