I looked at the relevant article
in the wiki, however it doesn't seem to be a problem with my nameserver (I can ping out just fine). The ntp servers are supposed to be listed in /etc/ntp.conf, however this file doesn't exist. What does exist is /etc/default/ntpdate. This file has its own list of ntp servers (one actually, ntp.ubuntu.com) that it is supposed to use if /etc/ntp.conf doesn't exist.
So, the command ntpdate just returns
17 Apr 18:33:34 ntpdate: no servers can be used, exiting
whereas I can explicitly give the command a server and it works fine
root@debian:~# ntpdate ntp.ubuntu.com
17 Apr 18:34:14 ntpdate: adjust time server 184.108.40.206 offset 0.018658 sec
Funny. Does anyone have this problem?