So, if it isn't enough for you that it's now possible to see the view from almost any road in the world while sitting at your computer, today Google announced a new Street View feature. If there's a clock in the upper left-hand corner of an image, it means you can see what that scene looked like up to seven years ago.
To use the feature, you start by just clicking on the clock. You'll then be presented with a window that lets you move a slider back through time to 2007, with thumbnails of the scene changing as you do so. If you want to see any of those thumbnails full-screen, you click on it. Simple as that.
The feature was introduced today, and can be tried out via the first of the two links below. Needless to say, it only applies to locations that have been photographed for Google Maps Street View starting in 2007.