Definitely agree. We chose to use EmberJS for this exact reason. The idea of working offline and synchronizing changes back to your API backend when you're back online is great.

Offline apps have been doing this for ages -- it's great that web tech is finally catching up w/ these great adaptations of HTML5 features.

Who is we? Synchronizing changes back to the API doesn't sound easy especially when the state of the remote side may have diverged from the client.