I'm in a similar situation that I need help with. I took my OS drive with Snow Leopard on it and I put it in a external enclosure. I just bought a 2012 cMBP and installed a 256GB SSD and installed Mountain Lion via Apples servers. I just downloaded CCC and I want to clone the drive. My questions are:
A) Will CCC erase ML and install SL?
B) Will there be any OS related duplicate files (ie. two Application folders)?
I've never done this before so all help is greatly appreciated.
A) Yes it will. Then you will have a problem, because your Retina will not run on Snow Leopard.
B) No. A normal CCC clone deletes everything on the target drive and replaces it with what is on the source drive.
Here is what you should do. Start the Retina and then attached the old Snow Leopard drive in the enclosure. Now launch Migration Assistant (/Applications/Utilities) on the Retina and point it to the external disk to import your user account and all apps and data. When you are done you user account from Snow will now be on the Retina SSD will all apps and data right where is always was.
One caveat here. If you have already made a DRII account on the Retina and you also had the same name DRII account on the Snow Leopard disk, Migration Assist will try to import the account into itself and make a mess with duplicate folder etc. This would be a bad thing
.
To avoid this you need make a new temp account on the Retina, then delete the DRII account and run Migration Assistant from the temp account. This will pull the DRII in clean from the Snow disk. After you are done you can login to the DRII account and delete the temp account.
I am assuming here your data on the Snow disk is current and that is what you want to bring in intact on the Retina. If you have some other setup going on, tell me what it is and we can work out the best scenario for you.
The BEST way to do this is at the end of a new/clean OS install just run the Migration Assistant to import your data.