One of the cool new features that is going to be available in Longhorn was the thumbnail page of the document that shows up next to the scrollbar. It was captured in a photograph from Paul Thurrott's WinSuperSite.
This shows the mouse arrow moving across the scroll bar and the thumbnail appearing which is based upon the page that would appear at that scrollbar position. The cool thing about the thumbnails (using Aero) would be that the actual image of page would appear INCLUDING images and even running VIDEOS!!!! In fact, in this shot, it was a video that was showing in the thumbnail (without sound).