People who've been idle for a long time have probably
just forgotten to log out. Thus, they should be kicked
off so that they don't affect the choice of music for
those who are still around.
Some time before automatically kicking people (an
hour?), they should get a warning on their console.
I'm not married to the 12h number in any way, if you
want to pick some other number or make this
configurable (or just ignore it :-) that'd be fine with
me as well.