“If you see a clock icon in the upper left-hand portion of a Street View image,” explain the Googles, “click on it and move the slider through time and select a thumbnail to see that same place in previous years or seasons.”
This is kind of neat. From the Official Google Blog: “Starting today, you can travel to the past to see how a place has changed over the years by exploring Street View imagery in Google Maps for desktop. We’ve gathered historical imagery from past Street View collections dating back to 2007 to create this digital time capsule of the world.”