If you do web design work in an Enterprise, you pretty quickly run into people who don't understand that there are fundamental differences between web apps and desktop apps.
What Web 2.0 does is it lets us get around some of those limitations. When Web 2.0 is done right, the Ajax is going to mean that they can work on an 'online app' without loading pages all the time (or rather, without appearing to load pages all the time).
Combine that with some of the database in a browser capabilities, and, in theory, you could get around even more of the limitations. E.g. user closes the browser window before hitting submit means the data is lost = annoyed users = poor usability. But if you use the offline storage to save the fields then it isn't lost after all. Hooray!
But yes, Facebook is retarded. Build a better one I dare you. ... Please.