Hooray! This is a great addition to the virtual sightseeing capability offered by Google Earth. Their just-released upgrade (version 4.3) allows you to see when the images were taken. As you move your cursor around the screen, the image date appears in the gray-shaded “status bar” at the bottom of the image:
Knowing the date of the imagery makes it a lot more informative. This example shows a large industrial facility (probably for processing natural gas) a few miles southeast of Farmington, New Mexico, in an area of intensive drilling for coalbed methane. The status bar indicates that this image was taken on March 26, 2007.