Ok I just want to update my post to give some information to folks with the same problem.
I made an appointment with the genius bar and they took my retina macbook for tests. They told me they were going to replace the logic board to eliminate the freezing issue. There were two weeks and a half now since it's been replaced, and no freezing since then. I assume they fixed the issue by replacing the logic board.
However, in the logs I found one kernel message "kernel: **** Debug info for *possible* hang in MAIN graphics engine ****", but no freezing occured. I conclude they may have manufacturing defects. This is a common problem guys. To to your local Apple store and ask them to fix the freezings. New macbooks MUST work flawlessly. Freezings are NOT normal.
PS you may stop the issue yourself by disabling the automatic switching of the graphic cards. I personally never observed freezings with the automatic switching disabled. Or ask Apple to fix the issue. You choice.