***Update*** The migration has been successfully completed: http://wpengine.wordpress.com/2013/07/09/dns-migration-successfully-completed/
Here is the latest news in the Zerigo DNS issues resulting from a DDoS on their servers today.
Currently, four of six DNS servers are up and responding. We are currently still working with Zerigo to resolve the issues occurring with the service and restore full functionality to the DNS servers.
You can view the status here: http://www.zerigostatus.net/
We’re also going to look into the cause of this and take appropriate steps to prevent this from affecting your sites again in the future.
Thanks for your continued patience as this issue is resolved.