72 hours? That's an eternity! There must (or should) be a better way! I really think that DNS is an outdated technology. Changing servers should be almost instantenious, not taking 72 hours.It can take up to 72 hours for a change in DNS to spread across the internet.
Well it has to trickle down from the main servers to the ISP or local servers. There wouldn't be a delay if all the DNS servers didn't cache stuff, but that would cost a lot of bandwidth. People running local servers though can just lower the cache lifetime and these changes will be received sooner.