Clock won't keep time after Mavericks installation
Ok, the solution has been identified:

Here are the steps


Replace Mavericks' buggy usr/sbin/ntpd executable with the one from your backups or other Mac with the previous version of OS X.
Delete var/db/ntp.drift
Restart the ntpd process using the new executable


I can verify that the clock now stays in sync. It's an absolutely ridiculous solution to a simple problem but it works. Thanks Gary at the Apple forum for the solution and emailing me the new executable. Also thanks to input from bmike above.