I was coordinating my house clocks using a NIS server until....it was down for several hours. I'm a bit of a nut about having the little machines monitor their own operation and reboot as necessary and when the NIS server went down, I lost my clock because it rebooted at the end of every retry interval. That prompted me to get a (relatively) cheap GPS module and take time from the satellites. That is working really, really well. In my case I provide the time from a single clock over my ethernet network and a XBee broadcast. That way I can sync devices based on either protocol. The little GPS module has a RTC in it too so I don't have to be as careful about reboots.
Your clock is a really cool device. Doing it from the ground up is impressive and fun. I would have made the cancel button about 100% larger though; my aim is bad in the morning.