Apple's highly anticipated 3.0 firmware release is causing us some operations problems right now. Large numbers of devices have been updated within a short time period, and it appears that after the update the sync code in the phone triggers a 'resync'. This puts extra load on our service which is currently running at maximum capacity. We've enabled load throttling measures which should ensure it remains working, but unfortunately not all devices will be able to sync until the load spike passes.
UPDATE: We've deployed some hardware upgrades tonight and service is now back up and running normally. We're expecting to be able to handle the load peak forecast for Thursday morning as the remaining iPhone users update their devices.