Well, normally time drift is a normal thing in computers (and most other devices), losing a small fraction of time, over time, but 14 minutes in only 23 days is really drastic (that's how long the server has been up since the last reboot). I thought I had installed ntpdate, a utility that regulary syncs *nix machines with a network time server, but I guess I didn't.
It's installed now, so except for being an hour off during DST (phpBB bug), time should stay relatively on track.
Edit: Actually, now that I think about, since nothing was ever syncing the clock, even a reboot wouldn't cause the clock to resync, so the server has probably been losing fractions of seconds ever since we moved to the new server.