Didn’t start out to enable offline synch - instead was just to make AJAX apps better. For example he wrote an app that could encrypt data on the client but then NOT let the server decrypt. You need to store the key on the client to decrypt again but cookie would not be a good place to store it.
Oooh, it might be time to dust off Secure Syndication. The key could be stored in the Database and the decryption could be offloaded to the WorkerPool to avoid hanging the UI.