EDIT: added Yosemite (it's exactly the same as for Mavericks).

Creating an USB installer for Mac OSX Mavericks or Yosemite is a little different than previous releases. The InstallESD.dmg no longer contains the complete bootable installation files, so writing that image to an USB stick is no longer a valid option.

There's now a tool within the downloaded OSX Mavericks or OSX Yosemite app which creates a bootable volume with all the required files for installation from a media. You can then unleash the command on any mounted volume (including disk images), provided they are big enough. For USB or other flash media, you'll need at least 8GB or more.

For this to wor  ...