Safer to just use cron-apt to download updates, then you can run apt-get dist-upgrade later.
Never a good idea to allow automatic updates in Stable, it's insane to do automatic updates in testing or unstable.
Also a good idea to have both apt-listbugs and apt-listchanges installed.
If you want you can install:
unattended-upgrades - automatic installation of security upgrades
Still not a good idea on testing or unstable.
Easier and safer to just create an alias for apt-get update && apt-get dist-upgrade -yd
Then look to see what is being updated/installed/removed. If everything looks OK then you run
Although you should be using aptitude, it is the recommended tool to use in Debian.
aptitude user's manual - http://algebraicthunk.net/~dburrows/...titude/doc/en/