Developer Chpwn, who has developed other successful jailbroken iPhone apps, has released Infiniboard in the Cydia Store, allowing iPhone users to scroll their springboard (the iPhone’s home screen) vertically. I tired out the application briefly on a first generation iPhone 3G running 3.0 and the app seemed to behave quite smoothly. The name also indicates that you will be able to scroll vertically infinitely on the springboard. Below is a screenshot of the preference pane for Infiniboard as well as link to a video of the app in action.
Have you tried Infiniboard? Do you think this is a feature that would work well natively on the iPhone or iPad, possibly in OS 4.0?