How do I make a seamless transition from my old blog to my new blog when updating my DNS?
DNS changes can take up to 96 hours to propagate around the Internet, so during that time some people will see the old blog and some will see the new.
If you don’t currently use WordPress and host it yourself, the experience will be funny for a few days as your DNS moves from the old server to the new.
Generally speaking, DNS updates take only a few hours. While doing your migration, turn off comments on your old WordPress install to prevent database writes (and potential data loss) during the process.