My solution...
Every time a user asks for help on a fresh and clean install, a lot of people questions out why you want to do that, the reasons are many, one of them is a hard drive (HD) replacement. For those who work in motion graphics, animation, video editing or simply for the pleasure to get the most of your Mac, there are high performance HDs such as 7,200, 10,000 rpm (now very rare) and solid state (SD) drives that really makes your Mac fly. Of course, tons of RAM will help too.
Apple's strategy on removing the optical drive unit (ODU) on late 2012 hardware (Mac Mini, Mac Book Pro or iMac) brought out a lot of trouble when comes to a clean Mountain Lion (ML) install. This relies on the fact that ML cames pre-installed and Apple didn't supply a thumb drive (USB drive). If Apple just realised the millionaire cost of time and effort for an advanced users to get a Mac up and running by their specific needs, Apple would probably ship every Mac with a USB drive for restoring, just for the fact that not every one, in every country has a good internet connexion.
Now, what matters most. At this moment, definitely there's no way to get the ML installer unless you got a good internet connexion to download it, but for that, you need the Mac where you are going to install it. NOTE: If you try to download the installer from another Mac, it will get the common installation file and not the specific one for your new late 2012. Why is this? Because late 2012 hardware were released a few weeks after the installer was uploaded to the Apple Store, and as far as I know, Apple hasn't updated the installer.
So, there are two way to get your Mac up and running with a fresh install.
A. If you don't care on getting the installer for further use, follows these steps:
1. Attach your original HD, either mounting it again in the Mac or using an external case.
2. Restart the Mac, when you hear the chime, hold down Command+R or Command+Option+R to start Recovery HD, or simply hold Option key to display bootable HDs, there you'll see the Recovery HD.
3. Enter Disk Utility and if necessary erase target disk (where you want to install ML), or select Reinstall Mountain Lion, after that quit and continue with installation.
4. When prompted to, select the target disk and follow the screen instructions. You have to wait until ML installer downloads. This might take several hours, be patient.
5. After it finishes Mac will prompt for restart or do it automatically.
6. If everything went well, you will have a newly ML installed.
7. You're done!, follow instructions and fill up your data.
B. The hard way, use this method if you would like a copy of the installer for further usage. (I grab this info from "http://hints.macworld.com/article.php?story=20110831105634716&query=lion+usb")
1. Restart your Mac using the original drive, either attaching your original HD on an external case or mounting it back again in the Mac.
2. Open the Terminal and type the following command to get a list of your HD partitions and hit Enter:
diskutil list
3. Look for Recovery HD in the list and write down the identifier for that partition, it looks something like 'disk2s3':
4. Type the following and hit Enter (Replace [identifier] with the Recovery HD identifier you grab earlier):
distil mount readOnly /dev/[identifier]
In my Mac it would be: distil mount readOnly /dev/disk2s3
5. This have made the Recovery HD partition visible, so now we have to mount it. Type the following and hit Enter:
hdiutil attach "Volumes/Recovery HD/com.apple.recovery.boot/BaseSystems.dmg"
6. Now, you'll see the Mac OS X Base System image on your Desktop.
7. Double click the Install Mac OS X application and follow the instructions. This will start the download process of ML installer. Sorry, but you have to wait until it finishes, maybe sever hours depending on you internet connexion.
8. VERY IMPORTANT! Some people reports the installer to reboot just a few seconds after it finishes with the download, some others that it prompts for restart. Just to prevent an automatic installation and grab the installer files, open a Text Edit document or download TextWrangler and install it, either the case, create a new document, edit it, but don't save it. This will prevent the installer to automatically reboot the system.
9. Now, open any Finder window and look into the target HD, there will be a folder called something like OS X Install Data, inside there are several files and a DMG file called InstallESD.dmg. Burn the entire folder or copy it onto a thumb drive.
In most cases, you just have to drag InstallESD.dmg into DiskUtility and restore it onto a USB drive and voila!, you got yourself an installer, but didn't worked for my late 2012 Mac Mini (macmini6,2). When I booted up with the thumb drive my Mac displayed the prohibition symbol, indicating the installer can't continue and/or that the installer isn't compatible.
10. If the installer restart window is still active after you backed up the folder, restart and install normally. If you cancelled the installation and/or for some reason rebooted the system, startup your Mac using the original HD, let it boot and open the target HD using Finder, mount the InstallESD.dmg file and double click the app installer, follow the instructions this time the Mac won't download anything because now it is installing from the source.
11. If you see an error saying the installation can't continue, reboot and repeat step 10.
12. If everything went well, you'll be able to install ML normally.
13, Next time you need to reinstall, you just need to start the installer form where you backed up the folder OS X Install Data. Note that this folder does not boot, so you have to start up you Mac using again your original Mac drive, what a mess, right?
Lets hope Apple resolves this issue as fast as possible and upload an updated 'universal' installer in the Apple Store or (this would be the topical best solution) ships a thumb drive with the installer to all late 2012 Mac with no ODU owners to avoid redownloads.
Hope this helps out.
