Here is a simple patch to slimserver.pl (5.4.0) that add a command line option
to set the playlistdir pref. The code is similar to what is done for --audiodir.

This option helps for packaging slimserver in such a way that it's really usable
right after a default installation. At least that was my feeling while working
on a slimserver ebuild [1] (a package for Gentoo Linux): one of my goals was
that, with the service script, audiodir/playlistdir/cachedir have default
locations from the very first run, with correct access permissions (server is
launched non-root).

Thanks.

[1] http://bugs.gentoo.org/show_bug.cgi?id=73832