Playlist documents can be copied anywhere.
Library playlists are stored in the ~/Music/QMidi/QMidi_Library.sql file, which can also be copied anywhere for backup purpose.
NB: copying this stuff will NOT copy the related media files.
See also:
http://www.mixagesoftware.com/en/qmidi/qmidi_help.html > Media management.
Mixage Software
www.mixagesoftware.com
support@mixagesoftware.com