The documentation doesn't seem very clear about this, but can I rely on NSUbiquitousKeyValueStore to persist data locally when the device is not connected, or should I also use a NSUserDefaults?
From the iCloud design doc with regards to Key Value storage
Always effectively available. If a device is not attached to an account, changes created on the device are pushed to iCloud as soon as the device is attached to the account.
(in the table at the bottom of the page)