Interesting. Adobe (=Macromedia) is developing a kind of “Flash browser” that we can build internet applications with that will, as one of its great features, manage offline-online usage, ie. you can use it while offline *and* while online. Competition: lots, but also XUL, the technology that Firefox and also Songbird, an iTunes clone use.
This could become an interesting space, but right now, I would bet on XUL over Flash, simply because it is already there and is slowly being proven/tested in real life apps.