It works. LocalStorage API is pretty solid and widely supported, if you're doing some simple buffering to handle connectivity issues it's awesome, except that it prompts the user for permission to store data. WebSQL is solid where it's implemented, and IndexedDB is solid where it's implemented but unfortunately there isn't a lot of overlap (screw you apple). and AppCache works great, but figuring out how it works in the first place is annoying as hell.

Its rarely straighforward, but definitely usable