The maintenance for Title Update 6.1 is well underway. The new version of the game is available for download, but the server maintenance window has been extended twice from the initial four hours (starting at 08:30 GMT) to six hours, to currently nine hours.
On an unrelated note, I hear Massive is looking for more Quality Assurance and DevOps folks...
Update! As of 4:50 PM GMT the servers are up and working!
Grav was with by Trilby Media.