For VM installs, we use a preseed which sets the debconf priority to  critical. This disables questions from the installer, where we agree to the default anyways (or we have set an appropriate default via preseed).
After using this method since ages (literally) Mika noted that on the installed machines the debconf priority is still critical. This implies that apt-get installs did not asked us much. For example, MySQL/MariaDB is installed having a root user with empty password! Especially since the notion of critical seems to be a bit inconsistent between packages, this might be a serious pitfall.
Probably this didn’t had bad effects on our systems, but we have switched to priority medium (dpkg-reconfigure debconf).
