Off-line web applications are a big deal for many companies/projects such as Adobe/AIR, Mozilla/Prism, Google/Google Gears and possibly Microsoft/Silverlight.
Gears for mobile devices is initially available for Internet Explorer on Windows Mobile 5 and 6.
An interesting point is that they “plan to keep the Gears API consistent across all platforms”.
So Steve Jobs new something and designed the iphone with browser only applications.