[UPDATED] Google already had more satellite and aerial imagery available for free than anyone. Now, they’ve added a new feature to new Google Earth 5 that let’s you turn back the clock and see other imagery they have for locations around the world. Click on the little “Clock” icon in the upper middle (or the “View->Historical Imagery” menu item). A time slider appears (see below) showing available imagery. If other imagery is available in your current view, you see little tic marks on the slider. Drag the slider (or click the left/right buttons) to see earlier or (or even newer) imagery.
For example, here’s a shot of the famous “Bird’s Nest” stadium from the 2008 Beijing Olympics as it appeared under construction on February 17, 2007:
And, here is a video showing this all in action:
This feature is amazing! The amount of data Google is storing must be immense! Several instances of imagery for millions of square kilometers! You may be able to see how your house changed over the years, or see aerial pictures of cities from decades ago. Expect to see lots of posts on this new feature.
[UPDATE: Google has put up their own post with examples of historical imagery in action.]