Override your energy saving settings and stop the mac from ever sleeping
with tail -F /var/log/system.log > /dev/null &.
Again, useful to me for keeping remote ssh sessions open, and I
might use it in combo with
wakeonlan
to start doing secret things in the middle of the night.
Incidentally your mac also won't sleep at all if you're running console.app,
which does the same thing for a different file.