OK, so you want to create a USB-drive to install OS X 10.9 “Mavericks”. In previous versions of OS X, you could create an USB-installer by restoring the InstallESD.dmg found in the OS-package downloaded from the Mac App Store (MAS). This is no longer an option.
In Developer Preview 4, Apple introduced a createinstallmedia executable. You’l find it inside the downloaded OS X Mavericks in
/Contents/Resources/createinstallmedia. We’ll use this to create a USB installer.
After you download OSX Mavericks from MAS, the installer will launch. Just quit to halt the installation process. This will retain Install OS X Mavericks.app in your applications folder.
Ready USB media
Now ready the media you want to use for the installer. You’ll need at least 8GB, but you can of course use larger media.
Format the media as Mac OS X Extended (Journaled) with GUID partition mapping. Name it Untitled.
Create the installer
Time to launch the Terminal and enter
sudo /Applications/Install\ OS\ X\ Mavericks.app/Contents/Resources/createinstallmedia --volume /Volumes/Untitled --applicationpath /Applications/Install\ OS\ X\ Mavericks.app --nointeraction
The command must be run as admin, so type in your admin-password. Be patient and wait 15-20 minutes for the process to finish.
Restart and hold down the option-key to boot from the newly created USB installer.
You can name the volume whatever you like. Just make sure to specify the correct volume-name in the createinstallmedia command