Finding duplicate files spread over your hard disk can be a time consuming matter. A quick way of doing it is to use the util 'fdupes'.
fdupes scans your filesystem for duplicates and uses a hash to check for any duplicate files even if they have different filenames.
Its easy to use, and runs on the command line.
fdupes -r /home/dir
You can redirect output to a file, check the file entries before deciding on any action.
Its in the main Debian repository, so go get it and check your files for duplicates.