Where does ntpdate get its settings from and what is the "no servers can be used" error about?

After mucking around for most of the day, I have come to the following conclusion:

ntpdate-debian is the version to use if you want to use a config script, and in that case, you would edit the /etc/default/ntpdate file.

ntpdate cannot be used without arguments nor does it have a config file. If you want to use this to update, you have to state the ntp server in an argument, such as ntpdate ntp.ubuntu.com.  

NTPDATE_USE_NTP_CONF refers to /etc/ntp.conf file as defined:

Set to "yes" to take the server list from /etc/ntp.conf, from package ntp, so you only have to keep it in one place.

Your error seems to be something temporary.