Today I helped a customer who had a bad internal hard drive on his iMac. He is the owner of Drive Genius 3. This iMac was still booting to Mac OS X.  He decided to use Drive Genius 3’s duplicate feature and copied the internal 750GB hard drive to a external 1TB drive. The clone finished successfully and he was happy . He got a replacement 750Gb hard drive for his iMac and wanted to clone 1Tb hard drive back to the the new 750 GB hard drive. Drive Genius 3 duplicate feature does  a device copy and therefore did not work for the clone of the big hard drive to a smaller hard drive.