For me, that's an essential still-missing piece in the big picture.
This is the sort of applications that Tim O'Reilly refers to as "Level 2" applications in his recent "Levels of the Game: The Hierarchy of Web 2.0 Applications" - "The application could exist offline, but it is uniquely advantaged by being online".
I am currently listening to Esther Dyson speaking on the Office 2.0 conference, who just disclosed that she sees herself as an Office 1.0 kind-of-person - with one of the main reasons she cited being the inability of current Office 2.0 applications to work effectively offline. So, I guess this pain is rather universal.
Solving it effectively might require better support from browsers - a combination of simple, secure offline functionality plus "queued posts" - post this to this page (end-point) when I go online.