On the file replace dialog I'd like to be able to specify certain actions if the contents of source and destination files are identical. I would want: replace, skip and delete source file. Delete source file would leave the file dates and attributes on the existing destination file while still removing the source file from the incoming directory. For it to really be useful you would need to be able to take the same action for all duplicate files in the current operation. This would relieve the user from having to decide if the files are the same or not.
I'm thinking of the situation where you are moving large numbers of image or sound files to a directory that may already have copies of some of them. You don't want duplicates but you may have multiple files with the same name that are completely different also.
If you do a byte by byte comparison, rather than an MD5 checksum, the check could stop at the first difference. You could probably read a few thousand bytes at a time from each file.