Google Earth now supports the use of historical imagery -- back to 1945 in some areas -- that lets users see how certain areas have changed over time.
As described by Wikipedia, Google Earth is a virtual globe, map and geographic information program that was originally called Earth Viewer, and was created by Keyhole, Inc, a company acquired by Google in 2004. It maps the Earth by the superimposition of images obtained from satellite imagery, aerial photography and GIS 3D globe.
To access historical imagery, do one of the following within the Google Earth application:
Click View > Historical Imagery
Click the Clock icon in the toolbar above the 3D viewer.
The small vertical lines on the timeline indicate the dates of different imagery available for your location.
Looking at my neighborhood let me realize the truly horrendous amount of development that occurred between 1991 and 1992, as agricultural fields suddenly became covered with houses.
Time magazine displayed a number of interesting shifts, such as Nevada before and after the development of Las Vegas, New Orleans before and after Katrina, and glacial melting.