Seen in my screenshot to the right, this allows users to swipe to the left in the Camera application to view the photo roll. On the right, the Camera app continues to show a preview in the viewfinder, even as the previously-taken photos slides in from the left.
Gone are the days of of trying to tap the small preview image on the lower-right corner. This new feature makes accessing previously-taken photos and video much easier, and much faster. The swiping is very fluid on my iPhone 4 running iOS 5 beta 2.
The Camera app is just one example of Apple using iOS 5 as an opportunity to remove many of the small annoyances dealt with everyday by its mobile customers.
iOS 5 will be released this fall.