@stephenw10:
Conversely I would be less likely to do it on a work box just because the consequences of some yet undiscovered NTPd exploit would be so much worse. If my home firewall goes down for whatever reason I get grief but I'm unlikely to find the locks have changed when I get back. If a firewall I'm managing for a business goes down (or worse gets owned) because I opened NTPd to WAN as a public service that's a different matter. You could see this as simply increasing the attack surface of a the firewall which is never a good thing. If you want to run a public NTP server the firewall should not be your first choice. ;)
Or there's always the possibility some company could make a consumer router and hard code your IP address in the firmware and set a ridiculous refresh rate when it can't reach the server and end up having you be flooded by tons of NTP traffic, bringing your network to a grinding halt. (This actually happened to the University of Wisconsin, courtesy of Netgear: http://pages.cs.wisc.edu/~plonka/netgear-sntp/)
But as mentioned, at work, I would not be running this on the firewall. (We run an ASA at work, though I've mentioned switching to pfSense when the discussion of replacing it has come up. Though I believe the last word on it was simply increasing the memory on it instead, though I don't believe that has happened yet.) My FreeRADIUS (on FreeBSD) server would be the most likely candidate for being a stratum 1 server (currently I believe it's a stratum 3) unless I special built a machine specifically for NTP.