While you need to be careful with automated updates and especially upgrades in Ubuntu, security updates should be performed ASAP and they are *most of the time* safe.
If you want to get notifications only when a security upgrade is performed (recommended) then use:
common/debian/cron-apt-security-update-reinstall.sh email@example.com upgrade
Test the installationYou can force the process to run right away while changing the cron expression in /etc/cron.d/cron-apt, then inspect the log file in /var/log/cron-apt/log. You should get something like:
CRON-APT RUN [/etc/cron-apt/config]: Mon Oct 2 04:00:01 EDT 2012 CRON-APT SLEEP: 3322, Mon Oct 2 04:55:23 EDT 2012 CRON-APT ACTION: 0-update CRON-APT LINE: /usr/bin/apt-get update -o quiet=2 CRON-APT ACTION: 3-download CRON-APT LINE: /usr/bin/apt-get autoclean -y Reading package lists... Building dependency tree... Reading state information... CRON-APT LINE: /usr/bin/apt-get upgrade -u -y -o APT::Get::Show-Upgraded=true Reading package lists... Building dependency tree... Reading state information... The following packages have been kept back: linux-headers-server linux-image-server linux-server 0 upgraded, 0 newly installed, 0 to remove and 3 not upgraded.