Clean install of Mountain Lion from a memory stick on a new Macbook Pro . At first on the command line the machine name was "unknownb8fckdls8dscdd" so I hacked the /etc/hostconfig file adding "HOSTNAME=Retina1.local" now the command prompt says "Retina1.local sam$" sam is the correct user name.
I thought it was fixed but when I went to set up sharing I saw the "unknown" again as shown above.
It worries me that some other trouble may pop up later.
MacBook Pro with Retina display, OS X Mountain Lion (10.8.1)