A few years ago NETGEAR put the time server at the University of Wisconsin as the only NTP server some of their routers looked at. Once every second. There's a firmware update that changes the behaviour but how many people upgrade the firmware of their home network? SMC did the same thing to the Australian Commonwealth Scientific and Research Organization's National Measurement Laboratory. And now an enthusiast who runs a Danish NTP server to provide very precise time measurements to Danish ISPs says D-LINK is flooding it (D-LINK tells Kamp it disagrees and is waiting on legal advice). There's an update to NTP, rather charmingly called Kiss-o'-Death packets, that let a server tell a client to go away. Of course not all NTP implementations respect these...
This is the tragedy of the commons; the common resources contributed to the Internet only work if people are polite and use them when they're appropriate. If developers can't get these things right without laywers spanking them, there will be a good excuse for a two-tier Internet with paid-for prioritised packets and telcos increasing their control.
http://en.wikipedia.org/wiki/NTP_vandalism includes both information about the floods and an arguemnt about whether vandalism is a loaded term
http://www.lightbluetouchpaper.org/2006/04/07/when-firmware-attacks-ddos-by-d-link/ - Richard Clayton on the detective work
http://people.freebsd.org/~phk/dlink/ - Poul-Henning Kamp on the Danish time server