(A note of a wish.)
A background downlowder script for the available new packages would be convenient for situations with slow Internet connection, so that the system administrator doesn't has to wait for the downloads when he uses APT.
It should run smth like:
apt-get update && apt-get dist-upgrade --download-only --yes
while the system is up in order to prepare the packages for the moment when one might want to install them.
It could be run in regular periods (day/week/month), say, with cron.
But it's not simply this command if it should be usable: first, its traffic should have a very low priority.
Second, simply running with cron is not enough, because it depends on the network iface: it should be started/restarted when an appropriate network iface is brought up unless the last scheduled download (1 in a day/week/month) has been already completed.
Third, perhaps, sometimes APT would require smth like "Yes, really do this." to be typed (even in order to proceed to downloading).