Can I say... WOO HOO! I know this is old school and that old habits die hard, but really... in Lion we had to first duplicate a file... then save... then we would get a dialogue to "save the file as...".
Now in Mountain Lion, we can simply hold down the option key to get the Save As command back.
There is also a good article at TUAW noting this and additionally showing you how to customize your hot keys for these commands.