I really don't understand the reason of all the excitement behind the offline-mode of Firefox 3.0.
I've different feelings about it: maybe some application need the offline mode, imagine downloading all your RSS feed to a PDA, and then read them when going to work on train or subway, but is this a real offline mode, or just downloading things and reading them from the disk?
If you are building an application that has to interact with a central database, do you really need to build a winform application with an offline mode that let you add/change/delete things while disconnected and the synchronize all your work with the central server when you reconnect?
Are these offline mode features really needed by your users? Or are the users accessing the application only from their offices with a broadband connection? I think that 90% of this kind of application, now that we all the fancy user interaction goodies that help build a better experience, can be safely developed as web application that doesn't need to go offline.
Probably there are some specific applications for specific scenarios that could need that feature, but does the benefits you have are worth the overhead of designing a local storage, designing a locking strategy for data, synchronization, software installation and update?
What are your opinion about that? Does your application have an offline mode?