For this process to work, the following are required:
- A purchased copy of Mountain Lion in the /Applications folder
- An 8Gb USB stick
The first screen asks you to select which version of OS X you want to create a bootable USB stick for (10.7 and 10.8 are supported). I selected Mountain Lion (10.8).
The next screen asks you to confirm which OS X ML copy to use, since it picked the correct one for me, I just continued by selecting Use this copy.
This screen asks whether you want to create a DVD or a bootable disk, since I have no optical drive, the only option is to create a bootable disk.
Next I selected that I have an 8Gb USB stick.
Here it asks to pick which USB stick to use to create the bootable disk. I've already had my stick plugged in, it was named 'USB'.
Before actually erasing the contents of the USB stick, DiskMaker gives a warning, I selected Erase then create the disk.
The next bit takes quite some time (15 mins or so). DiskMaker will copy all of the required files to the USB stick now.
After the copy is completed, there is a final screen where you can make a donation for using the app, quit or open startup preferences.
Using Lion DiskMaker is a painless way of creating a bootable OS X Lion/Mountain Lion USB installer.
I give it 4/5 stars.