myth.find_orphans.pl is a perl script in the contrib directory for finding orphaned rows in the recorded table (entries which don't have matching media files) and orphaned media files (potentially taking up gigabytes of otherwise usable disk space) which have no matching row in the recorded table.
Note on option --host=
When using more than one MythTV backend and the option --host=<foo>, <foo> should be the name of the host connected to the TV tuner hardware. The script does not seem to support more than one backend with connected TV tuners yet. It only finds database entries for a single specified backend.