Should add an option for users to disable this (like remember me on login forms)... not good for public computers if you don't know the form you just filled in but didn't submit will retain the data. Other than that, cool!
Persisting localStorage seems to be controlled by the setting to delete cookies after exiting the browser. If i have it set to delete cookies, it deletes localStorage. if i allow it to keep cookies after quitting the browser, then it persists localStorage.
(Noticed this because the demo failed for me the first time.)