Wouldn't invest much time in a tool that is not available for download, to be honest.
Nevertheless it looks well done.
If you don't mind me asking, what country are you from?
I ask because I find this strange, since here in the San Francisco bay area, I find it difficult to get 'away' from an internet connection. They're everywhere I go, whether I want it or not. I carry an internet connection on my smartphone and can tether to it whenever I need it. The only time I can't get an internet connection is when I'm in the middle of the woods, and that's just because I'm not paying for AT&T.
Having authoring tools "in the cloud" is the premise for many great services such as Google Apps, Microsoft Office apps, Facebook, Wordpress, etc... Being able to do something as cool as HTML5 authoring without having to invest hundreds of dollars in some Adobe product has great value to many... especially students or young poor people that want to learn and don't want to pirate software to do it.
I develop on the go a lot, so I do find myself very often with either faulty connections or no connection at all.
there are two ways to address it. first of all we will add offline support at some point, so you can work offline and when you are online it will sync itself with the cloud.
another possibility we are considering is just to wrap it up into multiplatform desktop app which is technologically not is difficult to do these days.