We needed to take the servers down for around 24 hours to complete the data migration. We hate to have them offline, but the process goes much faster this way and causes less problems.
If you're wondering the technical reason for this, we're moving all of the data from flat files into a proper database: Couchbase. Once that is done, we can continue our work of sharding the login server.
We'll post another message when the process is complete. When we're back, everyone will be able to collect their Christmas presents (if you haven't yet) and we'll be doing double drops and other promos to celebrate. :)