At the Google Developer Day (end of last week), a big announcement was the new Google Gears browser add-on and API (now in beta). It's set to let you run apps like GMail in an offline mode, as well as any other web app that plugs into the architecture.
This is a pretty huge step for online apps, as the elephant in the room has always been how dead they are when you are offline - and everyone is offline at one time or another.
Angus Kidman over has a good exploration of the tech over at APCmag.com. Well worth a look for anyone who is interested in reading about the future of applications. Yes, that includes you...
Google Gears up for offline apps [APCmag.com]