I use mpd (for now [I] media-sound/mpd (firstname.lastname@example.org): The Music Player Daemon (mpd)) player with system-wide storage for playlists.
Some time ago I've updated my music collection and find, that default installation of mpd is non full-featured for unprivilleged user usage.
# id tux
uid=1001(tux) gid=1001(tux) groups=1001(tux),18(audio),85(usb),998(vboxusers),995(vboxsf),994(scanner),35(games)
Adding write permission for group:
# chmod -R g+w /var/lib/mpd/playlists
# ls -l /var/lib/mpd/ | grep list
drwxrwxr-x 2 mpd audio 4096 Jan 4 16:33 playlists
Please add setting this permission in ebuild.
Probably with the same for /var/lib/mpd/music directory.
Also it is strange to see logs in /var/lib/mpd/ instead of /var/log/…