Maybe it isn't really a new feature, but it is new to me! When you look at an area using Google Earth, if there are earlier photographs of the area available, you will see bar that lets you move back in time. Obviously, the resolution is limited to when photographs were taken, but it was very interesting to look back over pictures of the subdivision that I live in now and the subdivision I lived in previously, and watch the progression of development in these areas.
Some of the pictures go surprisingly far back. the Eiffel Tower had pictures going back to 1943, which I suspect were World War II reconnaissance photographs.