From facebook:

At midnight PDT (3 hours from now) we will be bringing the servers down for maintenance. The estimated downtime will be between 20 – 60 min. Thank you for your patience. ~RB

The server will be shutting down at 5pm Melbourne time this evening, and is expected to be offline for 20-60 minutes.

No information on what is actually being done during this time, but I figured people would appreciate the warning.

EDIT: The game came back up at 5:30pm, so it was down for about 30 minutes 🙂