Here’s a great tip for anyone using the latest Mac OS and wants to create recovery media that don’t rely on having a live internet connection to download the media from Apple each time…
Apple will not offer a USB or Optical Disk external installer to Mountain Lion (as far as we have heard). That does not mean you cannot sneaker net the install around your home, office or lab. Lion Diskmaker has been updated to allow you to make a bootable USB or SD Card installer on a 8GB piece of media.
On a Retina MacBook Pro with a 8GB SD Card, the process took about 10- to 15 minutes. From there, you can install local copies of Mountain Lion, even from scratch, without having a 4GB download each time. That saves a lot of time if you have many machines to update or do not have broadband.
via Apple Intelligence.