So I added by NTP server
ntp.hawaga.org.uk(that also does a bunch of other stuff), waited a while for the score to rise, and then sat back and watched the port 123 packets flow.
There is lots of fun stuff about NTP breaking in ways which result in server floods - summarised in Wikipedia's NTP_server_misuse_and_abuse
One accusation that I've seen is that 50% of traffic is well behaved clients, and that the other 50% is a small number of misbehaving hosts which poll and poll and poll and poll. I've seen that behaviour in some of my
tcpdumpruns, though that is not too bad today:
Over a 15 minute period, I got 282 packets, less that one per second, from 53 different IP addresses, with a very unbalanced distribution: 24 hosts sending one packet, 50 sending less than one per minute (15 packets total), 3 sending more than one per minute, and one host sent 65 packets.
Update (Jan 6th 2011): You can watch the score history for my server in my pool.ntp.org profile, although at time of writing its kinda dull, being a flat top score for the past few days.
Update (Jan 7th 2011): I grabbed packets for about the last 24, and see 2736 distinct IP addresses, 32778 packets total (8 packets avg), noisiest host was 126.96.36.199 with 4628 packets. Anyway that's the most number of users I've ever provided service to, I think!
Update (Jan 17th 2011): I now have MRTG monitoring this server's estimated offset from correct time (similar but different to the profile graph above):